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Electrical ENGINEER'S 

POCKET-BOOK: 



A HAND-BOOK 

OF VaSFUL DATA FOR ELECTRICIANS AND 

ELECTRICAL ENGINEERS. 



HORATIO Ar*FOSTER, 



WITH tup: collaboration of eminent specialists. 



FIFTH KDITION, 
COMPLHTELT REVISED AND ENLARGED. 



NEW YORK: 

D. VAN" NOSTRAND COMPANY 

1908. 






•l, 



/ 



I 



GOPYRTGHTED, 1902, 1908, BY 

D. VAN NOSTRAND COMPANY, 
New York. 



fStanbope f>rM« 

F. H. GILSON COMPAKY 
BOSTON. U.S.A. 



PREFACE TO THE FIFTH EDITION. 



In appreciation of the very cordial reception accorded 
the earlier editions of this book, and in recognition of 
the fact that vast changes and advances have occurred 
in every branch of electrical engineering since the 
original publication, the author feels called upon to 
issue the present revised and enlarged edition. 

The book as now presented, exceeds the previous 
editions in magnitude by about 600 pages, while the 
subject matter of every section has been either com- 
pletely revised and brought up to date, or entirely 
re-written. The aim throughout has been to supply 
in exhaustive and condensed form, the data essential to 
the engineer engaged in any of the branches of the vast 
domain of electrical engineering. While our concep- 
tion of the fundamental principles of electrical science 
can of necessity have undergone no very considerable 
alteration, those essential details which in effect con- 
stitute the working data of the practicing engineer 
have so altered and grown that books published only 
a fe#¥ years ago are already obsolete. It is believed 
that a stage in the progress of electrical engineering 
standardization has now been reached wherein a com- 
pilation such as the present can be accepted as embody- 
ing the vital element to which future advances will 
appear to a degree in the relation of superficial alter- 
ations. 

The original plan of dividing the subject into a 
number of sections and having each revised by an 

iii 

181662 



IV PREFACE TO THE FIFTH EDITION. 

eminent specialist in that particular field has again 
been followed. Aside from the easy accessibility 
afforded, this plan of construction is valuable only 
in proportion to the weightiness of the authorities 
entrusted with the revision of the several divisions, 
and it is confidently believed that a perusal of the 
names heading the sections will lead to the conviction 
that a more approved and authoritative organization 
could not have been wished for. The several con- 
tributors are widely known and recognized as among 
the first of their respective specialties, and it is be- 
lieved that the general average of excellence assured 
by their collaboration surpasses that of any compila- 
tion of the kind previously attempted. 

Each section is complete in itself, but needless 
repetition has been avoided by the free use of cross 
references through the medium of the very extensive 
index. 

Attention is directed to the large quantity of new 
matter, appearing for the first time in print, in the 
several sections. In the section on Conductors, e.g., 
the tables of Inductance, Capacity and Impedance, will 
be found new and original. Many sections, e.g., 
Street Railways, Photometry, Conductors, Lighting, 
Roentgen Rays, etc., are pointed out as examples 
of exhaustive though condensed presentation. The 
mechanical section has been treated with the same care 
and attention as the electrical. 

The matter has been confined to the requirements 
of the electrical trades and sciences, the inclusion of 
the usual mathematical tables and data found in the 
commonly used handbooks having been avoided. 
These tables being easily accessible, and the present 



PREFACE TO THE FIFTH EDITION. V 

edition being already of great magnitude, this exclu- 
sion will be appreciated. 

An important feature of the present volume will be 
found in the voluminous and studiously developed 
index and table of contents. The index is as com- 
plete as the limitations of manipulative facility will 
permit, and is calculated to render the finding of the 
particular phase of the subject sought a matter of 
least possible labor. The table of contents is designed 
to supplement and extend the use of the index, and in 
conjunction with the marginal thumb-index will render 
instantaneous the location of sections and subdivisions. 

The careful and lengthy work of revision and search 
leads the author to believe that the number of errors 
cannot be large, and he ventures to express the hope 
that readers discovering any will have the kindness 
to bring them to his attention. 

In conclusion the author begs to express his grati- 
tude to the many contributors for their cooperation, 
and to the publishers for their painstaking effort and 
g^enerosity in making so handsome and substantial a 
volume. 

HORATIO A. FOSTER. 

100 Broadway, New York. 
June 1, 1908. 



/ 



LIST OF CONTRIBUTORS. 



Smbob. unto, inrtnunent. { J^'p^iSlS^"'* 
M«URirem«nts { Sif.^&S'sheldJii. 



1 



Magnetic Properties of Iron 
Electromagnets 

Properties of Conductors . 
Properties of Conductors 
Carrying A.C. Currents . 

Dimensions of Conductors 
for IHstrlbution Systems . 

Underground Conduit Construction. 



Townsend Wolcott. 
Prof. Samuel Sheldon. 



> Harold Pender, Ph.D. 
(Harold Pender, Ph.D. 



Standard Symbols 
Cable TMIng . , 



Dynamos and Motors . . . 

Tests of Dynamos and 
Motors 

Alternating Current Ma- 
chines 



N.E. Contractors* Assoc. 

Wm. Maver, Jr. 

I Cecil P. Poole. 
< £. B. Raymond. 



E. B. Raymond. 
Cecil P. Poole. 



( W. S. Moody. 
( K. C. Randall. 



A.I.E.E. 



The Static Transformer . . 
Standardization Rules . . . 

*^„* "****^' '°*'°: I ^' C- H. Sharp. 

J. H. Hallberg. 



descent 
Electric Lighting, Arc 



vU 



VIU 



LIST OF CONTRIBUTORS. 



Illuminatitig Engineering 



Electric Bailways 



Electrolysis 

Transmission of Power 
Storage Batteries . . . 



Switchboards 

Lightning Arresters . . 
Electricity Meters . . 

Telegraphy 

Wireless Telegraphy 

Telephony 

Electricity In the U. S. Army 

Electricity In the U. S. Navy 

Resonance 

Electric Automobiles . . . 

Electrochemistry and Elec- 
trometallurgy .... 

X-Rays 

Electric Heating, Cooking 
and Welding 

Lightning Conductors . . . 

Mechanical Section .... 
" " Index . 



Dr. C. H. Sharp. 

'A. H. Armstrong. 

C. Renshaw. 

N. W. Storer. 

Milton W. Franklin, ALA. 

A. A. Knudson. 
Dr. F. A. C. Perrlne. 
Lamar Lsmdon. 

H. W. Young. 

B. P. Rowe. 
E. M. Hewlett. 

Townsend Wolcott. 



{ 



H. W. Young. ' 
J. B. Baker. 

Ghas. Thorn. 

F. K. Vreeland. 

J. Lloyd Wayne, 9d. 

Grahame H. Powell. 

J. J. Grain. 

Lamar I^rndon. 

C. J. Spencer. 

j Prof. F. B. Crocker. 
) Prof. M. Arendt. 

Edward Lyndon. 
{Max Loewenthal, E.E. 

Prof. Alex. G. McAdie. 
I W. Wallace Christie. 



Index 



Max Loewenthal, EJS. 



SECTIONS. 



Page 

SYMBOLS. UNITS, INSTRUMENTS 1 

MEASUREMENTS 66 

MAGNETIC PROPERTIES OF IRON 89 

ELECTROMAGNETS 108 

PROPERTIES OF WIRES AND CABLES 131 

PROPERTIES OF CONDUCTORS CARRYING A.C. CURRENT 238 

DIMENSIONSOFCONDUCTORSFOR DISTRIBUTION SYSTEMS 260 

STANDARD SYMBOLS FOR WIRING FLANS, N. E. C. A. . 290 

UNDERGROUND CONDUITS AND CONSTRUCTION .... 301 

CABLE TESTING 321 

DIRECT-CURRENT DYNAMOS AND MOTORS 334 

TESTS OF DYNAMOS AND MOTORS 378 

ALTERNATING-CURRENT MACHINES 404 

STATIC TRANSFORMER 443 

STANDARDIZATION RULES A. I. E. E 501 

ELECTRIC LIGHTING 528 

ILLUMINATING ENGINEERING 584 

ELECTRIC RAILWAYS 612 

DETERIORATION OF METALS BY ELECTROLYSIS ... 852 

TRANSMISSION OF POWER 864 

STORAGE BATTERIES 872 

SWITCHBOARDS 906 

LIGHTNING ARRESTERS 980 

ELECTRICITY METERS 997 

TELEGRAPHY 1040 

WIRELESS TELEGRAPHY 1066 

TELEPHONY 1069 

USE OF ELECTRICITY IN U. 8. ARMY 1123 

ELECTRICITY IN U. S. NAVY 1153 

RESONANCE 1216 

ELECTRIC AUTOMOBILE 1224 

ELBCrROCHEMISTRY AND ELECTRO-METALLURGY . . . 1229 

X-RAYS 1248 

ELECTRIC HEATING. COOKING, AND WELDING .... 1266 

UGHTNING CONDUCTORS 1277 

FOUNDATIONS AND STRUCTURAL MATERIALS 1289 

STEAM 1327 

WATER-POWER 1460 

SHAFTING. PULLEYS, BELTING. ROPE-DRIVING .... 1481 

MISCELLANEOUS TABLES 1499 

POWER REQUIRED TO DRIVE MACHINERY 1616 

INDEX 1633 

ix 



M 

/ 



TABLE OF CONTENTS. 



ELECTRICAL SECTION. 

STMBOLSk UHrfS, nrSTRUMEMTS. 

Page 

Beetrieal Engineerins Symbols 1 

Electrical Engineering Units 2 

Symbols for Phymcal Quantities (Table) 6 

latemational Electrical Units and Measurements 10 

Equivalent Units. Energy and Work (Table) 12 

(losed areoit Cells 14 

Open Orcoit Cells 15 

Dry Batteries 18 

Standard Cells 19 

Grouping of Battery Cells 19 

(ialvanometerB 21 

Reaistanoe Standards 30 

Wheatstone Bridge 31 

Water Rheostats 83 

(SalTanised Iron Wire, Properties of 34 

(Condensers 35 

SpedBc Inductive Capacity of Gases (Table) 35 

Spetific Inductive Capacity of Solids (Table) 36 

Specific Inductive Capacity of Liquids (Table) 37 

Specific Inductive Capacity 38 

Ekctioroeters 40 

VoitmetecB 40 

Ammetera 41 

i3eetro-Dynamometers 42 

WattmelecB 42 

Kdrin's Composite Electric Balance 43 

Potentiometer 47 

Inttruments and Methods of Determining Wave Formn 49 

QMliograph 60 

MBASURBMEIITS. 

Qemeotary Latvs of Electrical Circuits 55 

BflBstanoe Measurements 56 

Bflsistanoe of Galvanometers 60 

Bentanee of Batteries 60 

Beastanoe of Aerial Lines and House C&rottits 61 

Xi 



; 



XU TABLE OP CONTENTS. 



E.M.F. Measurements 02 

Capacity Measurements 63 

Electromagmetie Induction 64 

Coefficient of Self Induction 65 

M^wurement of Self Inductance 66 

Measurement of Mutual Inductance 67 

Measurement of Power in A.C. Circuits 69 

Testa with Voltmeter 74 

E.M.F. of Batteries . 74 

E.M.F. of Dynamos 74 

Comparison of E.M.F. of Batteries 76 

Resistance Measurement with Voltmeter 78 

Resistance Measurement with Voltmeter and Ammeter , . 78 

Measurement of Very Small Resistances 79 

Measurement of Insulation Resistances 80 

Measurement of Insulation Resistance of Dynamos 86 

Measurement of Insulation Resistance of Motors 87 

Measurement of Resistance of Batteries 87 



MAGNETIC PROPBRTIBS OF IRON. 

Data for (B-3C Curves (Table) 89 

Permeability at High Flux Densities (Table) 91 

Methods of Determining Magnetic QualHies of Steel an<l Iron ... 91 

Permeameters 94 

Core Losses 98 

Hysteretio Constants for Different Materials (Table) 99 

Hysteresis Loss Factors (Table) 99 

Hysteresis Factors for Different Core Densities (Table) 1(X) 

Hysteresis Tests 101 

Hysteresis Meter 102 

Eddy Current Factors for Different Ckire Densities (Table) 106 

Specific Energy Dissipation in Armature C!ore 107 



ELECTROMAGNETS. 

Principle of Magnetic Circuit 109 

Traction 110 

Magnetisation and Traction of Electromagnets (Table) Ill 

Winding of Electromagnets 112 

Resistance of Magnet Wire at 140*^ F. (Table) 112 

Relation between Wire Length. Siie and Turns per Volt (Table) ... 114 

Correcting Length of Magnet Coil (Table) 117 

Linear Space Occupieti by Single Cotton-Covered Wire (Table) ... 121 

Linear Space Occupied by Double Cotton-Covered Wire (Table) . . 123 

Alternating (Current Electromagnets 127 

Heating of Magnet Coils ' 127 

Law of Plunger Electromagnet 127 

PuU and Ampere-Turn Factors (Table) 12g 



TABLE OP CONTENTS. Xlll 



PROPERTIES OF WIRES AND CABLES. 

Page 

TJnite of Resistance 131 

Speoifio Resistance, Relative Resistance and 'Relative Conductivity 

(TaUe) 132 

Temperature Coefficient (Table) 133 

Fhyneal and Electrical Properties of Various Metals and Alloys (Table) 134 

Wire Gauces (Table) 141 

Wire Strands 142 

Fhyaeal Constants of Copper Wire (Table) 143 

Effect of Admixture of Copper with Various Subntances (Table) ... 144 

Copper Wire Tables 146 

Tenile dtrength of (Copper Wire (Table) 156 

Weight o£ Copper Wire (Table) 157 

UDderwriters' Test of Rubber Covered Wires 161 

Standard Rubber Covered Wire Cables 161 

SUodard Conductor, National Electric Code, G. E. (Table) 162 

^ledal Oeblee for Car Wiring (Table) ' 173 

Xavy SUndard Wires (Table) 174 

Paper Insulated Cables (Table) 174 

(^mbric Insulated Cables (Table) 179 

Telephone Gebles (Table) 188 

Teksraph and Submarine Cables (Table) 189 

JointB in Rubber Insulated Cables 190 

Jointing Gutta-Percha 0>vered Wire 193 

Ahiminom Wire (Table) 194 

Ahmunum and Ck>pper Compared (Table) 195 

Ccwnparative Cost of Aluminum and Copper for Equal Cond. (Table) 195 
Comparison of Aliuninum and Copper for Equal Length and C]!on- 

doctivity (Table) 196 

ReslBtanoe of Solid Aluminum Wire 62% Conductivity (Table) ... 196 

Stnnded Weatherproof Aluminum Wire (Table) 197 

Dimensione and Resistance of Stranded Aluminum Wire (Table) . . 198 

Aluminuzn for Higb Tension Transmission Lines 199 

Iron and Steel Wire, Phyeical Constants (Table) 199 

Double Galvanised Telegraph and Telephone Wires (Table) .... 200 

GalTanised Signal Strand. Seven Wires (Table) 200 

Ptopertica of Steel Wire (Table) 201 

BeslBtanoe Wires, Spec. Res. and Temp. Coeff. (Table) 202 

Gennan Silver 202 

Resistances of German Silver Wire (Table) 203 

Ibnganin 203 

Electrical Properties and C!onstitution of Manganin (Table) 204 

Dimeosions. Resistanoe and Wei^ts of Resistance Wires (Table) . . 204 

ResBstance Ribbon. la la, C^xiality 206 

Krapp's Resistanoe Wires (Table) 206 

Renetanoee of Driver-Harris Resistance Wires (Table) 207 

Ckirrent Ganying Capacity of Wires and Cables 208 

Ckrrsring Capacity of Wires for Interior Wiring (Tables) 209 



X17 TABLE OF CONTENTS. 



Carrying Capacity of Rubber Insulated Cables (Table) 210 

Heating of Cables in Multiple Duct Conduit 210 

Watts Lost in Single-Conductor Cables (Table) 212 

Current Carrying Capacity qf Lead-Covered Cables . 213 

Fusing Effects of Electric Currents 217 

Tension and Sag in Wire Spans 218 

Calculation of Vertical Sag 222 

Properties of Dielectrics 227 

Dielectric Strength of Rubber 229 

Dielectric Strength of Gutta-Percha 202 

Dielectric Strength of Air 233 

Puncturing Voltage of Mica (Table) 234 

Minimum Sise of Conductors for High Tension Transmission .... 235 

PROPERTIES OF CONDUCTORS CARRTHTG ALTERNATHfO CURRERTS. 

Skin Effect Factors at 20^ F. (Table) 237 

Self Induction and Inductive Reactance of Circuits 23S 

Self Induction of Iron Wire 240 

Self Induction of Solid Non-Magnetic Wire (Table) 241 

Inductive Reactance of Solid Non-Magnetic Wire (Table) 242 

Inductive Reactance of Loop of Three-Phaae Line (Table) 245 

Inductive Reactance of Solid Iron Wire (Table) 248 

Capacity, Capacity Reactance and Charging Current of Transmission 

arcuitB formed by Parallel Wires 248 

Capacity of Transmission Circuits formed by Parallel Wires (Tables) 252 

Simple Alternating Current Circuits, Definitions 259 

DDfBllSIONS OF CONDUCTORS FOR DISTRIBUTION SYSTEMS. 

Kelvin's Law 261 

Calculation of Transmission Lines 204 

Effect of Line Capacity 264 

FormuIsB for Ooes Section, Weic^t and Power Loss (Table) .... 265 

Cross Section, Resistance and Reactance Factors (Table) 266 

Capacity Susoeptanoe of Two Parallel Wires (Table) . 269 

Numerical Examples of Calculations of Wiring Systems 271 

Transmission Line of Known Constants 274 

Transmission Line FormulsB (Table) 275 

Parallel Distribution 277 

Calculation of Ooss Section, Weight, etc., of Lines 277 

diart and Table for Calculation of Alternating Current Lines .... 279 
Determination of Size of Conductors for Parallel Distribution of Direct 

Current ." 284 

Transposition of Lines 285 

Loss in Sheath of Three-Conductor Lead-Covere<l Cables 293 

Bell Wiring 293 

Gas Light Wiring 296 

Wiring for Generators, Motors, Transformers, etc 295 

Wiring for Induction Motors 296 

Connections of Transformers for Wiring 297 



TABLE OF CONTENTS. XV 

STAHDARD SYMBOLS FOR WnUHO FLAHS AS AOOPTBD BT THE 
HATIOHAL ELECTRICAL CONTRACTORS' ASSOaATIOH. 

UHDBRGROUHD CONDUITS AND. CONSTRUCTION. 

Page 

Cost of Manholes in DolUre (Table) 302 

Cost of Sewer ConnectionB in Dollan (Table) ... 303 

Cbostant Cdst per Conduit Foot for Manholes in Dollare 304 

Cbst of Paving per Square Yard in Dollars (Table) 305 

Cost of Street Excavation per (}onduit Foot (Table) 306 

Constant Cost per Conduit Foot in DoUara (Table) 306 

Cost of Duct Material in Place (Table) 307 

Cost per Conduit Foot in Gties (Table) I 307 

Cndergiound Work at New Orleans (Table) 308 

Boston Edison O). Construction 309 

Itemixed Cost of Conduit (Table) 316 

Eaiinukting Cost of 0>nduit (Table) 317 

Estimating Cost of Manholes (Table) 317 

Grouping of Ducts in Manholes 318 

UoderRTOund Cables 319 

CkUe Heads 320 

CABLE TESTING. 

loBolaaon Resistance Tests 321 

Testins Joints of Cables 323 

Capacity Teats of Cables 324 

Locating Breaks by Capacity Tests 327 

Locating Crosses in Cables 327 

Locating Faults in C^les 328 

Copper Resistanoe or Conductivity of Cables 330 

Testing Submarine (}ables During Maqufacture and Layiiiic 331 

Locating Faults in Underground Cables 331 

High Voltage or Dielectric Tests of Cables 332 

DIRECT-CURRENT DYNAMOS AND MOTORS. 

NotaUon ... 334 

Fundamentals 336 

External Characteristics 337 

MagneUc Distribution 340 

Armatures 341 

Armature Windings 342 

Balancing the MagneUc Circuits in Dynamos 349 

Heating of Armatures 349 

Armature Reactions 350 

Commutators and Brushes 351 

Field Magnets 352 

Cboiing Surfaces of Field Magnets (Table) 352 

GTToetatie Action on Dynamos in Ships 352 

Direct-Current Motors •■ 353 

Lsooard's System of Motor Control 354 






XVI TABLE OF CONTENTS. 

Page 

Three- Wire System for Variable Speed Motor Work 354 

Practical Dynamo DesifEn 355 

Armature Details 356 

Armature Loeoee 358 

Commutator and Brushes 361 

Air Gap and Pole Face 363 

Field Macneta 364 

Dynamo Efficiency 370 

Armature Slot Sices for Arranisement of Standard Wires (Table) . . 372 

Trial Armature Coil Slot Depths (Table) 373 

Trial Values for Minimum of Armature Coils (Table) 373 

Trial Values for Maximum Turns per Coil (Table) 374 

Trial Values for CurrentOarrying Capacity of Armature Conduotoie 

(Table) 375 

Barrel Armature Winding Constants (Table) 376 

Average Magnetic Leakage Coefficients (Table) 376 

Average Dynamo Efficiencies (Table) 377 

TESTS OF DYNAMOS AHD MOTORS. 

Temperature Tests 378 

Overload Tests 381 

Insulation Tests 381 

Strain Tests 381 

Regulation Tests of Dynamos, Shunt or Compound, and Alternators . 382 

Regulation Tests of Motors, Shunt, Compound and Induction .... 383 

Efficiency Tests of Dynamos 383 

Core Loss Test and Test for Friction and Windage 383 

Brush Friction Test 384 

Separation of Core Loss into Hysteresis and Eddy Chirrent Loss . . . 385 

Kapp's Test with Two Similar Direct-Current Dynamos 387 

Electric Method of Supplying the Losses at Constant Potential . . . 380 

Calculation of Efficiencies 391 

Hopldnson's Test of Two Similar Direct-^^hirrent Dynamos 303 

Fleming's Modification of Hopkinson's Test 394 

Motor Tests 394 

Test of Street Railway Motors 397 

Tests for Faults in Armatures 402 

ALTERNATING-CURRENT MACHINES. 

Energy in an Entirely Non-inductive and Balanced Threc-Phase (cir- 
cuit 405 

Energy in Non-inductive Thrce-Phaae Circuits 406 

Copper Loss in Armatures of Alternators 407 

Compensated Revolving Field Alternators 409 

Regulators for Alternating (Xirrent Generators 409 

Alternating (Xirrent Armature Windings 410 

Armative Reaction of an Alternator 414 

Synchronisers 416 

Inductor Tjrpe Synchroscope • 417 

Note on the Parallel Ruiming of Alternators 410 



• • 



TABLE OF CONTENTS. XVU 

Page 

Byndironisins 421 

Alternating Current Motors 421 

Elementary Theory of the Polyphase Induction Motor 422 

AnalsrticBl Tlieory of Polyphase Induction Motor 423 

Speed of Rotary Field for Different Numbors of Poles and for Various 

Frequencies (Table) 424 

Slip of Induction Motors (Table) 426 

Core of Stator and Rotor 426 

Number of Sots in Field-Frame of Induction Motors (Table) .... 426 

Rotor Slots for Squirrel Cage Induction Motors (Table) 427 

Flux Densities for Induction Motors (Table) 427 

Rotor Windings 429 

^rnchronous Motors 430 

Theory of Synchronous Motor 432 

Dynamotors 434 

Direct-Current Boosters 436 

Rotary Converters 436 

Value of Alternating Current Voltage and Current in Terms of 

Direct Current (Table) 438 

Cbnverter Armature Windings 441 

QMinertion of Transformers and Rotary Converters 442 

Oxrrent Densities of Various Materials 442 

THE STATIC TRANSFORMER. 

Gores of American Transformers 443 

Tiansfonner Elquations 446 

Features of Design 447 

Insulation 447 

Temperature 447 

Efficiencies 453 

Magnetic Fatigue' or Aging of 8teel and Iron 455 

Change of Hysteresis by Prolonged Heating (Table) 457 

Regulation 458 

Onnparative Expense of Operating Large and Small Trausformers 458 

P6wer Factor 468 

Testing Transformer 459 

Sparking Distances Across Needle Points 462 

Transformer for Constant Secondary Current 462 

Economy Coils or (>ompensators 463 

Transformers for Constant Current from 0>nBtant Potential 464 

General Electric 0>nstant Current Transformers 464 

Reactaooe for Alternating (Xirrent Arc Circuits 466 

iy>tentaaJ Regulators 467 

Separate Circuit Regulators 469 

Three-Phase Regulators 469 

Three-Fhaae Transformers 470 

Ratio of Transformation in Three-Phase Systems 471 

Tiaosformer Connections 472 

Sagle-Fliaae Transformer Connections 472 




XVlll TABLE OF CONTENTS. 

Two-Phaae Transformer Connections 473 

Three-Phaae Transformer Connections 473 

Arrangement of TransformerB for Stepping Up and Down for Long 

Distance Transmission 475 

Three-Phase to Six-Phase Connections 475 

Methods of Connecting Transformers to Rotary Converters 476 

Converter and Transformer Connections 477 

Measuring Power in Six-Phase Circuits 477 

Y or A Connection in Transformers 478 

Grounding the Neuttal 478 

Unstable Neutral 479 

Rise of Potential 479 

General Electric Company Mercury Arc Rectifiers 480 

Westinghouse Mercury Arc Rectifier Outfits 481 

Transformer Testing 482 

Insulation Test 483 

Core Loss and Exciting Current 486 

Measurement of Resistance 486 

Impedance and Copper-Loss Tests 487 

Heat Tests 489 

Regulation 491 

Efficiency 498 

Polarity 495 

Data to be Determined by Testa 495 

Methods of Testing Transformers 496 

Specifications for Transformers 498 

Rise of Temperature 498 

Location of Transformeni 499 

Transformer Oil 600 

STAITDARDIZATION RULES OF THE AMERICAN INSTITUTE 

OF ELECTRICAL ENGINEERS. 

Definitions and Technical Data 502 

Performance, Specifications and Tests 605 

Voltages and Frequencies 522 

General Recommendations 622 

Appendices and Tabular Data 523 

ELECTRIC LIGHTING. 

Light and Laws of Radiation 528 

Intrinsic Brightness of Different Sources of Light (Table) 529 

Units and Standards of Light 530 

Photometers 534 

Incandescent Lamps 640 

Distribution Curves 540 

Current Taken by Various Lamps (Table) 642 

Proper Use of Incandescent Lamps 644 

Life and Candle Power of Lamps 644 

Importance of Good Regulation 646 



TABLB OF CONTENTS. XIX 

Page 

Guidle-Houn — Regulatioii of Lamp Values 646 

VariatioD io Candle-Power and Efficdency 647 

Lamp Renewals 647 

Luzninosity of Incandescent Lamps 648 

Metallised Carbon or Gem Lamps 649 

Tantalum Lamps 649 

Tan0rten Lamps 658 

Effect of Caianges of Voltage 658 

When and How Incandescent Lamps are Used (Table) 666 

Tbtals of Averafce Oonsumption, Showing Yearly Consumption per 

16-cp. Lamp Connected (Table) 655 

ODof>er-Hewitt Mercury Vapor Lamp 658 

Neni0t.lamp 662 

Tests of Various lUuminants by National Electric Light Assn. . . . 664 

Moore Vacuum Tube Light 665 

Efficiency of Moore Tube 666 

Are Lamps and Arc Lii^ting 668 

CUasiBeation 61 Arc Lights 568 

Open Are Lamps ^ . . 669 

Hi^ Tension Lamp 570 

Magnetite Arc Lamp 570 

Flaminc Arc Lamps 572 

Searchlight Projectors 675 

Eodoeed Arc Lamps 575 

Terts of Arc Light Carbons 577 

Endosed Are Carbons 578 

Sins of Oarbons for Arc Lamps (Table) 578 

Carbou for Searchlight Projectora (Table) 579 

Carbons for Focusing Lamps (Table) 579 

(handle Power of Arc Lamps 579 

Arc Lii^t Efficiency 580 

Heat and Temperature Developed by the Electric Arc 581 

Balancing Resistanoe for Arc Lamps on Constant Potential Circuit . 581 

Street Lic:hting by Arc Lamps 582 

light Cut Off by Globes 582 

Trimming Arc Lamps 583 

QXUMIRATIlfG ENGHfEERIlfG. 

Intensity of Illumination at Various Points (Table) 586 

Grafrfiic Illuminating Chart 587 

Required Illumination for Various Classes of Service (Table) .... 589 

Skvinff by the Use of High-Efficiency Lamps (Table) 589 

Experimental Data on Illumination Values 592 

CoefficieDts of Reflection 693 

Comparative Values of Illumination and Efficiency of Various Methods 

of Lifting (Table) 594 

Interior Illumination 596 

Data on Arc Lighting Installations in Operation (Table) 598 

Illumination ^99 






XX TABLE OF CONTENTS. 

Page 

Correct Use of Light 600 

Dietribation of Li^t by iDcandescent Lamps 601 

Concealed Lighting Systems 601 

Illumination Intensity Required for Reading 602 

lighting Schedules 608 

Lighting Table for New York City 604 

HouxB Artificial Light Needed Each Month (Table) 606 

Humphreys' Lighting Tables 607 

Hours of Burning Conuneroial Lights (Table) . 611 

Graphic Lifting Schedule for London, Eni^and . . . ^ 611 



ELECTRIC RAILWAYS. 



• 



Grades and Oirves 612 

Systems of Operation 613 

Car Equipments 613 

Locomotives 614 

Weights of Rails (Table) 615 

Radius of Curves for Different Degrees of Curvature (Table) .... 617 

GradesiifperCent. and Rise in Feet (Table) 617 

Elevation of Outer Rail on Oirves (Table) 617 

Equipment Tables 018 

Durability of Railroad Ties (Table) 619 

Paving 619 

Estimate of Track Laying Force 619 

Railway Turnout 620 

Electric Railway Automatic Block Signalling 622 

Requirements of a Signal System 623 

Typical Automatic Two-Line Wire, Non-Interfering Block Signal . . 624 

Distributed Signal Block System 627 

Material for One Mile Overhead Line Street Railway (Table) .... 628 
Estimated Cost of One Mile Double Track Overhead Street Rail- 
way System 629 

SUndard Iron or Steel Tubular Poles 629 

Standard Pole Line Construction 630 

Double Track Center Pole CJonstruction 631 

Plate Box Poles 632 

Tubular Iron or Steel Poles (Table) 633 

Oibic Ointents of Wooden Poles (Table) 633 

Average Weights of Various Woods (Table) 634 

Dip in Span Wire 634 

Side Brackets 635 

Trolley Wire Suspension 637 

Guard Wires 639 

Catenary Trolley (Jonstruction for A.C. Railways 640 

Properties of Galvanised Steel Strand Cable (Table) 642 

Line Material per Mile of Tangent Track for Catenary Construction 

(Table) 643 

Staggering Trolley for Sliding Contact 644 

Bracket Construction 644 



TABLE OF CONTENTS. XXI 

Span Gonstruetion 644 

Hangers per Span for Tangent Track (Table) 646 

Hangera per Span for PuJl-Off Curve Construction (Table) 647 

Energy Consnmption 652 

Cowtants for Determining H.P. of Traction (Table) 663 

florae Power of Traction (Table) 654 

Traction (Table) 655 

Revolution of Wheels for Various Speeds (Table) 665 

Fb«er for I>ouble and Single Truck Cars (Table) 656 

Tractive Effort on Grades (Table) 657 

Kilowatts on Grades (Table) 657 

Bower Consumption, 25 M.P.H., 85-Ton Car (Table) 668 

Number of Can on Ten Miles of Track, Various Speeds and Head- 
ways (Table) 658 

Effect of SSiape of Moving Body on Air Resistance (Curves) .... 659 

Headway, Speed and Total Number oi Cars 660 

Kles per Hour in Feet per Second and Minute (Table) 660 

Rating Street Hallway Motora 661 

Tractive Effort :..!... 661 

Thtftive Coefficient 662 

IVain Performance Diagrams 668 

Aeoderation 664 

Goostenction of Speed-Time Curve 666 

Data for Distance-Time Carve (Table) 669 

Data for Speed-Time Curve (Table) 671 

Rating Railway Motors from Performance Curves 678 

Hotor Capacity (}urve 676 

Graphical Approximation of Energy for Electric Cars 679 

Train Friction Curves 679 

Speed and Energy Chirves 680 

Motor Cbaracteristic Curves 685 

Determination of Energy 706 

Single-Phase A.C. Railway Motors . 707 

G. E. C^o/s Hand Potential Control System 710 

SUigle-FliBse Motor C^haracteristios 713 

Weights of A.C. Motor Equipments 719 

Comparative Weights 75 H.P. 4-Motor Equipments 719 

High Speed Trials on Lake Electric Railway 719 

Interurban Car Tests 722 

Train Los (Tables) 723 

Oomparison of Car Tests (Table) 724 

PenonaJ Factor of Motormen, Local Runs (Tables) 724 

Tests of Interurban Cars. Northern Texas Traction Co. (Table) . . . 725 

Two Motors va. Four Motors per Caa (Table) 729 

Railway Motors, Standard Sises and Ratings (Table) 729 

Weights of Equipment, Control Apparatus, Car Wiring and Motors 

(Table) 730 

Torque and Horse Power (Table) 731 

mcy Braking of Cars 731 






XXn TABLE OF CONTENTS. 

Page 

Copper Wire Fuses for Railway arcuits (Table) 731 

Approximate Dimensions of Electric Cars (Table) 732 

Weight of Car Bodies and Trucks 734 

Dimensions of Brill Cars (Table) . . . ' 737 

Electric Locomotives 789 

Installation of Electric Car Motors 745 

Preparation of the Car Body 746 

Installing Controllers 746 

Wiring 746 

Operation and Care of Controller 747 

Diagrams of Car Wiring . . . ' 747 

Equipment Lists 752 

Controllers 753 

Series Parallel Controllers 755 

Electric Brake Controllers 755 

Rheostatic Controllers 756 

Dimensions of ControUera (Table) 757 

Sprague G. £. Multiple Unit Control 761 

Westinghouse Unit Switch S3«tems of Multiple Control 766 

Approximate Rates of Depreciation on Electric Street Railways . . 770 

Depreciation of Street Railway Machinery and Equipment 770 

Car Heating by Electricity 770 

Track Return arcuit 771 

Type of Bonds 772 

Welded Joints 778 

Resistance of Track Rails (Table) 770 

Relative Value of Rails and Bonded Joints 780 

Ingredients of Rails Under Test (Table) 780 

Board of Trade Regulations for Great Britain 781 

Calculation of the Overhead Conducting System of Electric Rail- 
ways 785 

Continuous Current Feeders Load Determination 780 

Economical Design of Feeders 786 

Limiting Potential Drop 788 

Two Classes of Feeders 788 

Calculation of Dimensions of Conductors 791 

Drop and Loss in Line Between Two Substations of Unequal Poten- 
tial 794 

Impedance of Steel Rails to Alternating Chirrent 795 

Experimental Determination of Impedance of Steel Rails 795 

Experiment on Inter works Track of Westinghouse E. and M. O). . . 796 
Comparative A.C. and D.C. Resistance Trolley and Track per Mile 

of Circuit 798 

Tests of Street Railway Circuits 798 

Tests for Drop and Resistance in Overhead Lines and Returns . . . 798 

To Read the Ground Return Drop Directly 799 

To Determine Drop at End of Line 800 

To Determine the Condition of Track Bonding and the Division of 

Return Current 800 



TABLE OP CONTENTS. XXIU 

Page 

Teiting Rail Bonds 801 

Street Railway Motor Teating 803 

Dnw-Bar Pull and Efficiency Test without Removing Motor from 

Ckr 803 

Testing Drop in Railway Circuits 804 

Street Car Faults and Remedies 805 

Wiring Diagrams for Lighting (Srcuits on Street Care 800 

Special Methods of Distribution 807 

Three- Wire System 807 

Booster System 807 

Retom Feeder Booster 808 

Beetric Railway Booster Calculations 809 

Series Boosters for Railway Service 813 

Sbbstation System 814 

Fbrtable Substations 819 

Tlard Rail Systems 821 

Rentanoe of Rails with Varying Composition 821 

Beetrical and Chemical Qualities of Steel for Third Rail (Table) . . 822 

Wrought or Refined Iron for Third Rail (Table) 824 

Resistance of Steel, Variation with Manganese (Table) 825 

Resistance of Steel. Variation with Carbon (Table) 826 

Reristance of Steel, Influence of Carbon (Table) 826 

Renstance of Steel (Table) 827 

Location of Third Rail 830 

Third Rail Insulators 831 

Third Rail Shoe 832 

New York Central Third Rail 834 

Estimated Cost of One Mile Single Track Protected Third Rail. Approxi- 
mate 836 

Conduit Systems of Electric Railways 835 

Sorfaoe Contact or Electro-Magnetic Systems 840 

Westini^ouse Surface Contact System 841 

Sectional Rail Construction S46 

(jencral Electric Contect Railway System 847 

DSTERIORATION OF UKDERGROnND METALS DUE TO 

ELBCTROLTTIC ACTION. 

Destnietive Effects 853 

locrease of Current Flow upon Mains Due to Bonding same to Rails 

or to Negative Conductors 856 

eminent Movements upon Underground Mains 858 

Beetrolytic Effects upon Water Meters 855 

Dancer from Fire or Explosions 858 

Qectrolysis in Steel Frame BuikHn^B 859 

Current Swapping 859 

Ahemating Chirrent Electrolysis 860 

Insulating Joints in Mains 861 

Surface Insulation 862 

Summary 863 



XXIV TABLE OP CONTENTS. 



TRAHSMISSION OF POWBR. 

Engineoring Features 804 

Relative Efficiencies of Various Traosmiasion Methods (Table) . . . ' 8S5 

Special Features of Design Due to Transmission Line Requirements . 868 

Motive Power 807 

Storage Reservoirs 867 

'Generators 870 

Transmitting Apparatus 870 

Transformers 871 

Pole Lines 871 

STORAGE BATTERIES. 

Theory and General Characteristics 872 

Voltage 874 

Types of Plates 874 

Capacity 874 

Discharge Rate Curve 876 

Voltage Variation 876 

Electrolyte 877 

Cadmium Test 878 

Polarisation 879 

Efficiency 879 

Comparison of Plants and Pasted Rlectrotien 880 

Charging 880 

Removal from Service 881 

Battery Troubles 881 

Testing 882 

Weight of Complete Cell and Component Parts 882 

Dimensions 883 

Rates of Charge and Discharge 883 

Capacity at Various Discharge Rates 883 

Voltage Curves 883 

Internal Virtual Resistance 883 

Variation in Density of Electrolyte 884 

Loss of Charge with Time 884 

Efficiency at Various Char^re and Discharge Rates 884 

Erection of Battery 884 

Usee of Batteries 886 

Methods of Controlling Discharge 889 

End Cells and Switches 890 

Counter E.M.F. Cells 891 

Resistance Control 891 

Shunt, Automatic, Reversible and Non-Reveraible Boosters 891 

Comparison of Boostere 897 

Installations 897 

Three- Wire Sj^tems 899 

Battery Capacity 900 

Strength of Dilute Sulphuric Acid of Different Densities (Table) . . 904 



TABLE OP CONTENTS. XXV 

Page 
Oooductinc Pbwer of Dilute Sulphuric Aoid of Different Strengths 

(Table) 905 

GDnducting Power of Acid and Saline Solutions 906 

SWITCHBOARDS. 

Design of Direct-Oontrol Panel Switchboards 906 

Copper Bar Data (Table) 911 

Alaminum Bar Data (Table) 911 

Altematiiig-Current Switchboard Panels 912 

Equipment of Single-Phase Feeder Panels 916 

Equipment of Three-Phase Feeder Panels 917 

Equipment of Two-Phase Feeder Panels 918 

Equipment of Induction Motor Panels . '. 918 

Equipment of Three-Phase Synchronous Motor Panels 919 

Equipment of Three-Phase Rotary Converter Panels 919 

Equipment of Constant-Current Transformer Panels 922 

Are Switchboards 922 

Direct-Current Switchboard Panels 924 

Hsod-Operated Remote-Control Switchboards 928 

Central Station Electrically Operated Switchboards 928 

GrcumstanceB which Indicate the Necessity of Installing Klertrically 

Operated Switchboard Apparatus 929 

Hydro-Electric Generating Station Design 930 

Bos-Bar and Bus-Bar Structures 933 

(Seneral Arrangement of Switchboard Devices 935 

Isolation of Conductors ' 936 

Cdfa for Voltage Transformers 988 

Hig^-Tension Conductors 939 

Cbntrolling and Instrument Switchboard 940 

Sabntataon Switchboard Equipments 942 

Switchboard Instruments and Meters 945 

Method of Figuring Instrument Scales ' 946 

Brief Guide for Writing Switchboard Specif! cations .947 

Switching Devices 948 

SfMridng at Switches .948 

CSrrait Breakers 949 

Circuit Breaker Design 952 

A.C. Ser\ice Circuit Breakers 952 

Capacity of Circuit Breakers f Dr D.C. Generators 955 

Cireuit Breaker Adapted for Motor of Given Size (Table) 955 

Sgnalling Relays 955 

Regulating Relays 956 

Protective Relays 956 

Applieation of Relays 960 

Lever Switches 963 

Plug Tube Switches 966 

Disconnecting Switches 965 

SvitdiM for High Potential 967 

Westinghouse Oil Circuit Breakers 969 

Oil (Srcuit Breaker Controller 975 

General Electric Oil Switches 976 



{ 



XXVI TABLE OF CONTENTS. 

I lighthing arresters. 

Li^tnins Protection Q80 

Switching Q80 

Cables 981 

Engine or Water Wheel Governor Troubles 081 

Protection Against Abnormally High Potentials on A.C. Circuits . . 981 

Use of Reactive Coils 982 

Use of a Protective Wire 982 

Ground Connections 983 

Lightning Arresteis 983 

Lightning Arresters for Direct Current 984 

Lightning Arresters for Alternating Current 987 

Non-Arcing Metal Lightning Arrester 989 

Garton Arrester 990 

S.K.C. Arrester 990 

Static Discharges 992 

Arresters for High Potential Circuits 993 

Low Equivalent A.C. Lightning Arrester 994 

Horn Type 995 

ELECTRICITY METERS. 

Action of Integrating Meters 997 

• Direct-Current Commutator Type Meters 997 

Thomson Recording Wattmeters 998 

Westinfi^ouse D.C. Int^n^ting Meters 998 

Duncan Meters 998 

Induction Type Alternating Current Integrating Meters 999 

Wattmeters on Inductive Circuits 1000 

Power Factor Compensation 1002 

Minimizing Effect of Voltage Variation 1002 

Westinghouse Single-Phaae Induction Wattmeters 1003 

Wflstinghouse Polyphase Induction Wattmeters 1003 

Thomson Hig^ Torque Single-Phaae Induction Wattmeteni .... 1005 

Thomson Polyphase Induction Wattmeters 1005 

Sangamo D.C. Integrating Meter 1006 

Elementary Diagram of Sangamo D.C. Meter 1007 

Sangamo A.C. Meter 1008 

Wright Discount Meter . 1008 

Meter Bearings, Registers and Commutators 1009 

Prepayment Wattmeter 1010 

Integrating Wattmeter Testing 1013 

Testing Service Meters 1015 

Calibration Data for Westinghouse Integrating Wattmeters (Table) . 1016 

Testing Meters for Accuracy on Inductive Loads 1018 

Method of Testing Service Meter for Inductive Load Accuracy ... 1019 

Obtaining Inductive Load from Two-Phase Circuits 1019 

Obtaining Inductive Load from Three-Phase Circuits ...... 1020 

Testing Meters 1020 



• « 



TABLE OF CONTENTS. XXVll 

Page 

Tntiog Fblyphase MeteiB 1020 

Standards for Testins Polyphaoe Meters 1020 

Senrioe Goniwetions of Polyphase Meters 1023 

Practical Methods of CSiecking Conneotions of Polyphase Meters . 1026 

Meter Testing Formula) 1028 

Formula for Testins the Shallenberger Ampere-Hour Meter .... 1028 
Testing Formula for Shallenberger and Westinichouse Integrating 

Wattmeters 1028 

Testing Constant of Westinghouse Meters 1029 

Westinghonse Direct-Current Meters 1030 

Table of Testing Constonis for G. E. Co.*8 Meters 1030 

* D3 '* Fblyphase Meters 1081 

Formula for Testing Duncan Recording Wattmeters 1031 

Table of Duncan Constants " K " and Watts per Rev. per M ... . 1031 

IVr cent Error Table for Fifths of a Second 1032 

Table Values of Constants for Fort Wayne Single-Phase Meters . . 1083 

Formula for Testing Sangamo Wattmeters 1035 

Tables of Constants for Sangamo Wattmeters 1035 

Graphic Recording Metere 1036 

Bristol Recording Meters 1036 

General Electric Graphic Recording Meters 1037 

Westin^ouse Graphic Recording Meters 1037 

Action of Meters 1039 

TELEGRAPHY. 

Amoican or Closed Circuit Method 1040 

European or Open Circuit Method 1040 

Repeaters 1041 

Umiken Repeater 1041 

Gbegan Repeater 1042 

Weiny-Phillipfl Repeater 1043 

Duplex Telegraphy 1044 

Dupleac Loop System 1047 

Half-Atkioaon Repeater 1048 

Doplex Repeater 1049 

Steam Duplex 1050 

Qnadruplex 1051 

Tdegrai^ Codcfl 1062 

WIRELESS TELEGRAPHY. 

Electrical Oscillations 1055 

E3eetromagnetic Waves 1055 

Antenna 1058 

Cbheicr 1058 

Syntonic Signalling 1059 

Skin Effect 1061 

Tranmitten , • • • ■ 1062 

Reeeivers 1064 

Detectors 1066 

Undamped Ownllations 1068 



XXVUl TABLE OF CONTENTS. 

TELEPHONY. 

tleoeivera 1070 

Transmitteni 1071 

Induction Coil 1074 

Hook Switch 1075 

Calling Apparatus 1075 

Series and Bridging Systems 1076 

Polarised Bell 1078 

Construction of Magneto Generator 1076 

Factors Affecting Transmission: Inductance, Capacity. Resistance . 1079 

Earth Currents, Induction, Cross-Talk 1081 

Metallic arcuits 1081 

Open Wire arcuits 1082 

Cables 1082 

Sample Specification for Telephone Cables 1083 

Capacity of Aerial Telephone Cables (Table) 1085 

Capacfty of Underground Telephone Cables (Table) . 1086 

Sises of Cables (Table) 1086 

Annual Expenses of Telephone (tables 1087 

Lii^tning Arresters 1087 

Classification of Telephone Lines 1088 

Central Office 1089 

Requirements of Satisfactory Operation of Switchboard 1089 

Small Switchboards 1089 

Multiple Switchboard 1090 

Busy Test 1091 

Series-Multiple Switchboard 1093 

Branch Terminal or Bridging System 1003 

Transfer Systems 1094 

Relative Value of Multiple and Transfer Systems 1094 

One Central Office va. Several 1094 

Tninking 1095 

Method of Operating Circuit Trunks 1096 

Auxiliary Trunk Signals 1096 

Ring Down or Common Trunks 1096 

Common Battery System 1096 

Rudimentary CJommon Battery Circuits 1097 

Lamp Signals 1098 

Circuits of Common Battery Switchboards 1098 

Three-Wire System 1099 

Two- Wire System 1101 

(>onunon Battery Instrument Circuits 1102 

Party Lines 1102 

Selective Systems 1102 

Method of Obtaining Impulse Currents 1103 

Ontral Office Apparatus Auxiliary 1104 

Automatic Exchange Systems 1105 

Simultaneous Use of Lines 1105 

Limits of Telephonic Transmission 1107 



TABLE OF CONTENTS, XXIX 

P»g« 

NotM on Cost of Telephone Plant 1108 

Private Linee, Intereommunicatins;, and House Syatems 1108 

Common Return Intercommunicatinic Systems 1114 

Tiro-Wire Intereommunicating Telephone Systems 1120 

USES OF ELECTRICITY IN THE UNITED STATES ARMY. 

SesrehUgfats 1123 

Data ReiaUve to SeaKhttghts (Table) 1127 

Rniaii0§ Chronograph 1128 

Sehuits Chronoeoope 1130 

Schmidt Chronograph 1131 

Sqnire-Crdkore Photo-Chronograph 1133 

Manipulation of Coast-Defenae Guns 1134 

Electric Fuses 1134 

Defensive Mines 1137 

Fortress Telephones and Telegraphs 1140 

Field Telephones and Telegraphs 1140 

Telautograph 1141 

Wireless Telegraphy 1145 

Electric Ammunition Hoist with Automatic Safety Stop 1147 

XightSi^ts 1148 

Firing Mechanism for Rapid Fire Guns . . .• 1140 

ELECTRICITY IN THE UNITED STATES NAVY. 

General Requirements 1154 

Engine 1154 

Typical Results of Tests on Generating Sets (Table) 1150 

SpedficatiooB for Turbo-Generator Sets 1 150 

Turbine llflO 

(jenerator 1161 

Operation of Generator 1162 

Steam Piping 1163 

Switchboardb 1168 

Doable Dynamo Rooms 1166 

Wiring Specifications 1167 

Single Conductor (Table) 1160 

Twin Conductor (Table) 1170 

Methods of Installing Conductors 1170 

Lighting System, Lamp Specifications 1171 

U. S. Navy Standards for 100-120 Volt Lamps (Table) 1176 

U. S. Navy Standards for 200-250 Volt Lamps (Table) 1177 

Valves for Navy Special Lamps (Table) 1178 

Diving Lanterns 1 179 

Searchlights 1179 

Signal Lights 1181 

ArdoM System 1181 

Track Lights 1181 

Power System 1188 



XXX TABLE OF CONTENTS. 



Tests 1184 

Principal Requirements for Controlling Panels 1185 

Tarret-Turnins Gear 1187 

Ammunition Hoists 1191 

^^ ft 

Endless Chain Ammunition Hoists 1102 

Boat Cranes 1194 

Deck Winches 1196 

Ventilation Fans 1196 

Water-Tight Doors 1198 

Steering-Gear . 1200 

Interior Communication System 1202 

Range Indicators 1204 

Revolution Indicators 1204 

Telephones 1206 

Fire Alarms and Call Bella 1210 

Range Finder 1211 

Speed Recorder 1211 

RESONANCE. 

Formula for Alternating Current Flow 1217 

THE ELECTRIC AUTOMOBILE. 

Resistance Due to Gravity and Power Required 1224 

Resistance to Traction on Common Roads (Table) 1225 

Tires 1226 

Motors 1227 

Batteries (Tables) 1227 

Rules for Proper Care of Batteries 1228 

ELECTROCHBMISTRT-ELBCTROMETALLURGT. 

Electrolysis 1229 

Resistances of Dilute Sulphuric Acid (Tabic) 1229 

Resistances of Copper Sulphate (Table) 1231 

Resistances of Zinc Sulphate (Table) 1231 

Applications of Electrochemistry 1231 

Electrolytic (3iemistry 1231 

Electrotyping 1233 

Electroplating 1233 

Electrolytic Refining of Copper 1235 

Production of Aluminum 1239 

Production of Caustic Soda 1239 

Production of Metallic Sodium 1241 

Potassium Chlorate 1242 

Electrothermal Chemistry 1244 

Calcium Carbide 1245 

Manufacture of Graphite 1245 

Electric Smelting 1247 



TABLE OP CONTENTS. XXXI 

X-RAYS. 

Page 

Tabet 1240 

lUteoorative Tube* 1251 

Eacdtinc Source 1252 

Intemipten 1253 

FIuorasoopeB 1266 

BLRCTRIC HBATQIO. OOOKIHO AND WBLDIKG. 

Variout Methods of UtUixinc the Heat Generated by the Electric 

Corrent (Table) . . ; 1256 

Equivaleat Vahiee of Eleotrieal and Mechanieal Unite (Table) . . . 1258 

Oist of Electric Gookin« 1259 

(}Qat oi Heatinc Water to Different Temperatures at Various Rates 

for Current (Table) 1259 

Eflideacy of Electric Cooking Apparatus 1260 

Qxnparative Costs of Gas and Electric OmUdk 1260 

CbmparisoD between Gas and Electric Rates 1261 

Cbst of Operatins Electrically Heated Utensils (Table) 1261 

Duly Electric Cooking Record for One Week (Table) 1262 

Electric Irons for Domestic and Industrial Purposes 1263 

Onunercial Electric Laundry Equipment 1263 

Eleetric Heating 1263 

Radiators and Convecters 1268 

Energy Cbnsumption of Electric Heaters 1265 

Gamparison between Electric and Coal Heating 1265 

Beetrie Car Heating 1265 

Industrial Electric Heating 1269 

Beetrie Heat in Printing Shops 1269 

Soldering and Branding Irons 1270 

llttviog Water Pipes 1271 

Electric Welding and Forging 1271 

Electric Rail Welding 1273 

Eaeetrie Smelting 1274 

AaneaHng of Armor Plate 1274 

Hydro-Electrothermio Ssrstema 1274 

PoKDate 1275 

T«ted Fuse Wire (Table) 1275 

Installation of Fuses 1276 

LIGHTNING CONDUCTORS. 

Selection and Installation of Rods 1278 

Chimney Protection 1281 

Teitfl of Lightning Rods 1282 

Directions for Personal Safety During Thunder Storms 1283 

Economy of Isolated Electric Plants (Tables) 1283 

Dtta on Isolated Plants (Table) 1285 

Data on Isolated Planttf in Residences (Table) 1287 



\ 



XXXll TABLE OP CONTENTS. 

MECHANICAL SECTION. 

FOUNDATIONS AND STRUCTURAL MATERIALS. 

Page 

F6wer Station Construction (Chart) 1289 

Foundations 1290 

Mortan 1293 

Sand and Cement 1294 

Weight of Flat Rolled Iron (Table) 1295 

Weights of Square and Round Ban of Wrouisht Iron (Table) . . . 1297 

Weight of Plate Iron (Table) 1298 

U. S. Standard Gauge for Sheet and Plate Iron and Steel 1299 

Columns, Pillars and Struts 1800 

Strength of Materials laoi 

Moment of Inertia 1802 

Radius of Gyration 1808 

Elements of Usual Sections (Table) 1303 

Cast-Iron Columns 1806 

Transverse Strength 1808 

Fundamental FormuUe for Flexure of Beams 1808 

General Formulie for Transverse Strength of Beams (Table) .... 1809 

Approximate Greatest Safe Load on Steel Beams (Table) 1810 

Beams of Uniform Strength Throughout Their Length 1312 

Trenton Beams and Channels (Tables) 1318 

Size and Distance between Floor Beams (Table) 1815 

Properties of Timber (Table) 1816 

Tests of American Woods (Table) 1317 

Wooden Beams (Table) 1318 

Southern Pine Data (Tables) 1320 

Masonry 1322 

Brick Work (Tables) 1321 

Weight of Round Bolt Copper (Table) 1323 

Weight of Sheet and Bar Brass (Table) 1328 

Composition of Rolled Brass (Table) 1323 

Weight of Copper and Brass Wire and Plates (Table) 1324 

Galvanised Iron Wire Rope (Table) 1325 

Transmission or Haulage Rope (Table) 1325 

Iron and Steel Hoisting Rope (Table) 1320 

STEAM. 

Steam Boilers 1327 

Types of Boilers 1327 

Horee Power of Boilers 1327 

Heating Surface of Boilera 1328 

Grate Surface of Boilers 1329 

Efficiency of Boilers 1329 

Strength of Boiler Shells (Table) 1330 

Rules Governing Boiler Inspection 1332 



••< 



TABLE OP CONTENTS. XXXUl 

Page 

Boiler Stays and Bnuses 1338 

Boiler SeiUnsB 1334 

CbimMya (Tables) 1338 

dumney Constructioii 1339 

BloweiB for Foroed Draft 1344 

Pim for Induced Draft 1345 

Eiadi and Ingredients of Fiieb 1346 

ToUl Heat of GombuBtaon of Fuels 1347 

Temperature of fire (Table) 1340 

Amencan Woods (Table) 1340 

American Coals (Table) 1360 

Heating Value of Goah 13M 

Anthracite Coal (Table) 1351 

fiitominous Goal (Table) 1351 

Approximate Analysis of Goal (Table) 1352 

Anlyais of Coke 1353 

Siiaee Required to Stow a Ton of Coal (Table) 1353 

Wttght of Coal (Table) 1354 

Rcbtive Values of Coals and How to Burn Them 1355 

Wood as Fuel 1356 

liquid PuelB 1356 

Chemical Composition of Petroleum Oils 1357 

Cbmparative Costs of Oil and Coal (Table) 1358 

Mechanical Stoking 1350 

Water 1360 

Weight of Water (Table) 1361 

Water for Boiler Feed 1362 

flbhibilities of Scale-making Materials 1363 

Purification of Feed Water by Boiling 1365 

Table of Water AnalysM 1366 

Feed Pumps 1367 

Pomping Hot Water 1367 

Injectors 1370 

Ddiverics for Live Steam Injectors (Table) 1871 

Rste of Flow of Water Through Pipes (Tables) 1373 

Lose of Head Due to Bends 1374 

Feed Water Heaters 1375 

SsYinc by HeaUng Feed Water 1376 

Pomp Exhaust 1377 

Fuel EooDomisen 1378 

Steam Separators 1380 

SifetyValva 1382 

Rules for Conducting Boiler Teste 1384 

Determination of Moisture in Steam 1394 

Tlirottling Glalorimeter 1304 

Ikistuie in Steam (Table) 1396 

Separating Odorimeter 1308 

Qoslity of Steam Shown by Issuing Jet 1400 

Fsctors for Evaporation (Table) 1400 



XXXIV TABLE OP CONTENTS. 



Properties of Saturated Steam (Table) 1404 

Superheated Steam 1413 

CoDdeusation in Steam Pipes 1415 

Overflow of Steam from Initial to Lower PranureB (Table) .... 1416 

Steam Pipes 1417 

Flow of Steam Through Pipes (Table) 1417 

Equation of Steam Pipes (Tables) 1413 

Protection of Steam-Heated Surfaces (Table) 1421 

Relative Value of Steam Pipe Ooverin^i 1422 

Relative Ek»nomy of Different Thicknesses of Covering 1424 

Wrought-Iron Welded Steam Gas and Water Pipe (Table) .... 1427 

Lap- Welded Charcoal- Iron Boiler Tubes (Table) 1428 

Collapsing Pressure 1429 

Resistance of Tubes to Collapse 1420 

Table of Dimensions. High-Pressure Cast-iron Screw Flanges (Table) 1430 

Tensile Strain of Bolts (Table) 1431 

Pipe Bends 1431 

Standard Pipe Flanges (Table) 1433 

Steam Engines 1434 

Digest of Report on Standardization of Engines and Dynamos . . . 1435 

Standardised Dimensions of Direct-Connected Generating Sets (Table) 1438 

Summary of Tests of Steam Engines (Table) 1439 

Horse Power of Steam Engines 1440 

Cylinder Ratios in Compound Engines 1441 

Number of Expansions for CJondensing Engines 1441 

Mean Effective Pressure per Pound Initial Pressure (Table) .... 1442 

Condensers and Pumps 1443 

Ejector Condenser Capacities (Table) 1445 

Air Pumps 1446 

(Srculating Pumps 1446 

Cooling Tower Test 1447 

Gas Engines 1448 

Classification 1448 

Comparative Economy 1449 

Value of Coal Gas of Different Camlle Powers for Motive Power 

(Table) 1450 

(3as Engine Power Plant 1450 

Gs8 Engine Pumping Plant 1451 

Steam Turbines 1451 

De Laval Steam Turbine 1452 

Pareons Steam Turbine 1453 

Curtis Steam Turbine 1455 

Steam Table 1458 

ft 

WATER POWER. 

Synopsis of Report Required on Watcr-Powcr Property 1460 

MiU Power 1462 

Comparison of Columns of Water (Table) 1463 

Yearly Expense per H.P. on Wheel Shaft (Table) 1464 



TABLE OF CONTENTS. XXXV 

Page 

PMBore of Water (Table) 1465 

Biv«tod Steel Pipes 1466 

Data for FlumeB and Ditches . . . 1468 

Wooden Stave Pipe 1468 

Rireted Hydraulic Pipe (Table) 1469 

Theoretical Velocity and Discharse of Water (Tubles) 1470 

Flow of Water through an Orifice - 1471 

Measurement of Flow of Water in a Stream 1471 

Theory of Rod Float Gauging 1471 

ICnera' Inch Measurements 1473 

flow of Water over Weirs 1478 

Weir Table 1474 

CUcttlating the Hoxse Power of Water (Table) 1475 

Water Wheels 1476 

TWjiiMB 1476 

Impobe Water Wheel 1480 

SHAPTIlfG, PULLEYS, BELTING. ROPE-DRIVIKG. 

Shafting 1481 

Deaeetion of Shafting 1482 

Hone Power Transmitted by Shafting 1483 

Hone Power Transmitted by Cold-Rolled Iron Shafting 1484 

Hollow Shafts 1485 

Table for Lasring out Shafting 1486 

PoDeys 1487 

BdUng 1487 

Width of Belt for Different Horse Power 1488 

Hone Power Transmitted by Different Belts (Tables) 1489 

Rope Driving 1490 

Hone Power of Manila Rope (Table) 1491 

Table of Horse Power of Transmission Rope 1493 

Slip of Ropes and Belts 1493 

Stiaiia Produced by Loads on Inclined Planes (Table) 1494 

TVaosmission of Power by Wire Ropes (Table) 1495 

(Jain (Tables) 1496 

Labrication 1497 

hinting 1498 

MISCELLAlfEOUS TABLES. 

Weights and Measures. English and Metric (Tables) 1499 

Greek Letters 1605 

Aagnlar Velocity 1505 

Friction 1505 

Temperature or Intensity of Heat 1506 

Oomparison of Different Thermometers (Table) 1506 

Coefficients of Expansion of Solids (Table) 1508 

Specific Heats of Metals (Table) 1509 

Heat Unit Table 1510 



( 



/ 



xxxvi ta6le of contents. 

Specific Heat of Gases and Vapors (Table) 161 

Total Heat of Steam 151 

Mechanical Equivalent of Heat 1511 

Specific Gravity (Table) 1519 

POWER REQUIRSD TO DRIVE MACHIlfBRT, SHOPS AKD TO DO 

VARIOUS KIHD6 OF WORK. 

Prony Brake 1515 

Horse Power Formulas 1515 

Power Used by Machine Tools (Table) 1515 

Motor Power for Machine Tools (Tables) 1518 

Horse Power in Machine Shops, Friction, Men Employed (Table) 1523 

Cotton Machinery (Table) 1524 

Power Required for Printing Machinery (Table) 1525 

Power Required for Sewing Machines 1525 

Power Consumption in Industrial Blstablishments (Table) 1528 

Power for Electric Cranes 1627 

Operating Cost of Electric Elevators 1628 

Saving by Electric Drive 1529 

List of Tools and Supplies Used for Installing Electric Lis^ts and 

Dynamos 1530 

Material Required for installing Lamps 1531 

Thawing Frosen Water Pipes Electrically 1531 

INDEX 1633 



SYMBOLS. UNITS, INSTRUMENTS. 



CHAPTER I. 

« 

The followin£ Itet of symbols has been compiled from various sources as 
beUur those most commonly in use in the United States. Little variation 
wiUbe found from similar lists already publishtnl except the elimination of 
wme that may be considered exclusively foreign. The list has been revised 
by competent authorities and may be considered as representing the best 
Bssffe^ 



I, Length, cm. =r centimeter ; 

in., or ''=inch, ft. or ' = 
foot. 

Jf, Mass. gr. = mass of 1 
gramme ; kg. = 1 kilo- 
gramme. 

T,tj Time. 5= second. 

]>erlT«d: geometric. 

S, f, Surface, 
r, Volume, 
t, p. Angle. » 

Mechanical. 
V, Velocity, 
n. Momentum. 
«, Angular velocity, 
a, Acceleration. 

9, Acceleration due to gravity 

=32.2 feet per second. 
F, /, Force, 
r, Work. 
P, Power. 
<, Dyne, 10 3 = 10 dynes. 

ft. lb., 
H.p. , h. 
I.H.P., 
B.H.P., 
E.n.F.i 



k 



«. 



^ 



Foot-pound, 
.p. : HP, Horse-power. 
Indicated horse-power. 
Brake horse-power. 
Electrical horse-power. 
Joules' equivalent. 
PresBQre. 
Moment of inertia. 



Quantity. 

Current. 

Potential Difference. 

Resistance. 

Capacity. 

Specific Inductive capacity. 

Derived lHakC*«tic. 

Strength of pole. 
Magnetic moment. 
Intensity of magnetisation. 



3. 



Intensity of magnetixation. 

Horixontal intensity of 
«^rth*s magnetism. 

Field intensity. 

f lagnetio Flux. 

r^agnetic flux density or 
magnetic induction. 

Magnetizing force. 

Magnetomotive force. 

Reluctance, Magnetic re- 
sistance. 

Magnetic permeability. 

Magnetic susceptibility. 

Reluctivity (specific mag- 
netic resistance). 



JD«ri%'«d f lectromarttetlc. 



Resistance, Ohm. 
do, megohm. 

Electromotive force, volt. 
Difference of potential, volt. 
Intensity of current, Ampere. 
Quantity of electricity. Am- 
pere-hour; Coulomb. 
Capacity. Farad. 
Electric Energy, Watt-hour ; 

Joule. 
Electric Power, Watt ; Kilo- 
watt. 
Resistivity (specific resis- 
tance), Ohm-centimeter. 
Conductance, Mho. 
Conductivity (specific con- 
ductivity. 
Admittance, mho. 
Impedance, ohm. 
Reactance, ohm. 
Susoeptance, mho. 
Inductance (coefficient of 

Induction), Henry. 
Ratio of electro-magnetic to 
electrostatic unit of quan- 
tity = 3 X 10*® centimeters 
per second approximately. 

0jmbola 1m ir«»«'<^l ume, 

D, Diameter. 
Radiiis. 
Temperature. 

Deflection of gahranometer 
needle. 



n. 
A 
c. 






r, 
t. 



SYMBOLS, UNU'S, INSTRUMENTS. 



A^.n. 



I' 

A.M. 
V.M. 
A.C. 
D.C. 
P.D. 
C.G.S. 

B. AS. 



Number of ftnything. 

Circamfereuce — cQameter : 
8.141fi82. 

2irN = 6.2831 X frequency, ID 
alternating current. 

Frequency, periodicity) cy- 
cles per second. 

Galvanometer. 

Shunt. 

North pole of a magnet. 

South pole of a magnet. 

Ammeter. 

Voltmeter. 

Alternating current. 

Direct current. 

Potential dilference. 

Centimeter, Qramme, Second 
system. 

Brown & Sharpe wire gauge. 



K.p.m., 
U.Pi 




B.W.G., Birmingham Wire gauge. 



UttJuJ 
TncJnnr> 



Revolutions per mixinte. 
Oandlepower. 
Incandescent lamp. 

Arc lamp. 

Condenser. 
Battery of cells. 
Dynamo or motor, d.c. 
Dynamo or motor, a.o. 

Converter. 

Static transformer. 

Inductive resistance. 
Non-iudufitive resistance. 



CHAPTER U. 

Mjidex. ]f otAtloB. 

Electrical units and values oftentimes require the use of large numbers 
of many figures both as whole numbers and in decimals. In order to avoid 
this to a great extent the index method of notation is in universal use in 
connection with all electrical computations. 

In indlcatinga larffenumber. for example, gay, a million, instead of writ- 
ing 1,000,000, ft would by the index method bo written 10" ; and 3S.00O QOQ 
would be written 36 X 10». ' 

A decimal is written with a minus sign before the exponent, or, tA« = .01 
= tO-« ; and .00048 is written 48 x 10-». t^ . . t«b 

The velocity of light is 80,000,000,000 cms. per sec., and is written 3 x 10". 

In multiplying numbers expressed in this notation the significant figures 
are multiplied, and to their product is annexed 10, with an index equal to 
the sum of the Indices of the two numbers. 

In dividing, the significant flgnrcs are divided, and 10, with an index equal 
to the a»#«rence of the two indices of the numbers is annexed to the divi- 
dend. 

Fundant^atal Cntta. 

The physical qualities, such as force, velocity, momentum, etc., are ex- 
pressecl In terms of lenf/th^ mcuts^ time, and for electricity the system of 
terms in universal use is that known as the C. G. S. system, 
viz. : The unit of length is the Centimeter. 

The unit of mass is the Qramme. 
The unit of time is the Second. 

Expressed in more familiar units, the Centim^^ is equal to .3937 inch in 
lengtn ; the Qramme is equal to 15.432 grains, and represents the mans or 
quantity of a cubic centimeter of water at 4° C, or 39.2° Fah. ; the Secotirl is 
the HsiJkrov I^'^ o' ^ sidereal day, or the «b}bo part of a mean solar day. 

These units are also often called absolute units. 

Oerlved Oeomefric tJnlta. 

The unit of area or surface is the square centimeter. 
The unit of volume is the cubic centimeter. 

Oarived Iflecliantcal ITnltn. 

Velocity is the rate of change of position, and is uniform velocity when 
equal distances are passed over In equal spaces of time ; unit velocity Is a 
rate of change of one centimeter per second. 



ELECTRICAL EKGINEEKING UKITS. 



An/gniat Feleeiip is the angular distance about a center passed through in 
«K Mcond of time. Unit ansruiar velocity is the yelooity oX a body moving 
jseirenlar path, whose ramus is unity, and which would traverse a unit 
.Mgle is unit time. Unit angle is 57°, 17^ 44.8^' approximately ; i.e., an angle 
rnim are equals its radius. 

iMtmatum is the quantity of motion in a body, and equals the mat$ times 
P0 vthcitjf, 

JeeeUraiUm Is the rate at which velocity changes ; the unit is an aceel* 
tion of one centimeter per second per second. The acceleration due to 
iTity is the increment in velocity imparted to falling bodies by gravity, 
' a OBOsiiy taken as 32.2 feet per second, or 981 centimeters per second, 
▼slue diiiers somewhat at different localities. At the North Pole g=: 
1; at the equator g=978.1 ; and at Greenwich it is 981.1. 

Force acts to eliange a body's eondition of rest or motion. It is that which 
mds to produce, alter, or destroy motion, and is measured by the time rate 
f cliange of momentum produced. 

Tbe oait of force is that force which, acting for one second on a mass of 
le ^nunme, gives the mass a velocity of one centimeter per second ; this 
lit IS eallec^a dyne. The force of sravity or weight of a mass in dynes may 

) fooad by multiplying the mass m grammes by the value of ^ at the pai^ 

eolarplace where the force is exerted. The pull of gravity on one pound 

ibe United States may be taken as 446»000 dynes. 

V9rk is the product of a force into the distance through which it acts, 
unit is the erg^ and equals the work done in pushing a mass through a 
aee of one centimeter sgainst a force of one dyne. As the " weight" 

oaegnmmB is 1 x 981, or 961 dynes, the work done in raising a weight of 

e gramme through a height of one centimeter against the force of gravity, 

M dynes, equals 1 X 981=981 ergs. 

na kilogramme- meter 7=: 100000 x 981 ergs. 

'mac energy is the work a body is able to do by reason of its motion. 

^(AmtitU energy is the work a body is able to do by reason of its position. 

3to onit of energy is the erg, 

*ovtr is the rate of workiiig, and the unit is the wattz=. IdC ergs per sec. 
jte-p tmer is the unit of power in common use and, although a somewhat 

ifrary unit, it is difficult to compel people to change from it to any other. 

equate 33,000 lbs. raised one foot high in one minute, or S50 foot-pounds 
^leoond- 

ft.4b.= 1.356 X lO' ^rgs. 

Tatt= 10* ergs per second.. 

fcoree-power=6BO x 1.356 X 10* ergs = 746 watts. If a current of I am- 

EI I*R 
Sow through B ohms under a pressure of E volts, then =— = -=2^ = 

^represents the horse-power involved. 

b French *■*■ force de chevcU" =736 watts =542.48 ft. lbs. per 8ec.= 
H. P^ and 1 H.P. = 1.01389 '* force de chev<U:* 

The Joule ^^1/= 10' ergs, and is the work done, or heat generated, by 
tt ssoond, or ampere flowing for a second through a resistance of an ohm. 
ff=heat generated in gramme calories, 
/= current in amperes, 
£=e.mX in volts, 
J?=: resistance in ohms, and 
/= time In seconds, 
'J?=0u24/*iZt=0.24 Elt. gramme calorie* or therms. 

IEt=zniU=:~=:EQ=zJoule». 

\l horBe-iK>ver=650 foot-pomids of work per second, 
Joules =:^^BQ=: .7373 EQ ft. lbs. 

Heat Vmlte. 

BHHah Thermal Unit is the amount of heat required to raise the 
itore of one poimd of water one deg. F. at or near its temp, of max. 

.. 30.1**; = 1 pound-degree-Fah. = 251 .0 French calories. 

I Calorie is the amount of heat required to raise the temperature of a 



i 






4 SYMBOLS, UNITS, INSTRUMENTS. 

nuiflB of 1 gramme of water from 4° C. to 5*^ C. = 1 gramme-degree-oei 
grade. 

Water at 4° G. ia at its maximum density. 

Joules eqtUfXilent^ J, is the amount of energy equal to a heat unit. 

For a B.T.U., or puund-degree-Fah., J=zl.(37 x 10** ergs., or = 778 f< 
pounds. 

For one pound-degree — Centigrade, J=: 1.93 x 10>" ergs. 

For a ceiiorie /= 4.189 x 10^ ergs. 

The heat generated in t seconds of time is 

—J- = -J- , where .f =4.189 x 10', 
and /, Rt and E are expressed in practical miits. 

Blectrlcttl IJBita. 

There are two sets of electrical units derived from the fondamea 
C. Q. S. units ; yis., the electrottatic and the electromagnetic. The fin 
iMuied on the force exerted between two quantities of electricity, and the t 
ond upon the force exerted between a current and a magnetic pole. 
ratio of the electrostatic to the electromagnetic units has been carefully 
termined by a number of authorities, and is found to be some multiple 
sub-multiple of a quantity represented by &, whose value is approximat 
3 X 10^* centimeters per second. Convenient rules for changing from one 
the other set of units will be stated later on in this chapter. 

Eleccroatiatic VmIU. 

As yet there have been no names assigned to these. Their values are 
follows : 

The unit of quantity is that quantity of electricity which repels witi 
force of one dyne a similar and equal quantity of electricity placed at v 
distance (one centimeter) in air. 

Unit of current is that which conveys a unit of quantity along a cond 
tor in unit time (one second). 

C/nit difference of potential or unit electro-motive force exists between t 
points when one erg of work is required to pass a unit quantity of elootrie 
from one point to the other. 

Unit of reeittance is possessed by that conductor through which unit e 
rent will pass under unit electro-motive force at its ends. 

Unit of capacity is that which, when charged bv unit potential, will h* 
one unit of electricity ; or that capacity which, when charged with one v 
of electricity, has a unit diiference of potential. 

Specific inductive capacity of a substance is the ratio between the ca] 
of a condenser having that substance as a dielectric to the capacity oj 
same condenser using dry air at 0° C. and a pressure of 76 centimet 
the dielectric. 

Marn^ttc' (Jntta. 

Unit Strength of Pole (symbol m) is that which repels another simili 
equal pole with unit force (one dyne) when placed at unit distance 
centimeter) from it. 

Magnetic Moment (svmbol ^)1t ) if> the product of the strength of 
pole into the distance between the two poles. 

Intensity of Magnetization is the magnetic moment of a magnet dii 
by its volume, (symbol (J)« 

Intensity of Magnetic Field (symbol JC ) ^s measured by the force it l 
upon a unit magnetic pole, and therefore the unit Is that intensity ol 
wnich acts on a unit pole with a unit force (one dyne). 

Magnetic Induction (symbol (B) is the magnetic flux or the nnml 
magnetic lines per unit area of cross-section of magnetized materii 
area being at every point perpendicular to the direction of flux. It 
to the magnetixing force or field Intensity JC niultiplied by thept 
f&: the nnu is the gauss. 

Magnetic Flux (symbol «) is equal to the average field intensity mall 
by the area, its unit is the maxwell. 

MagnetUdng Force (symbol JQ, ) per unit of length of a solenoid 



BLECTBICAL SNOIXEERIXG UNITS. 



irlfl-i-L where N':=z the number of turns of wire on the solenoid : X = 
dw loigth of the solenoid in cms., ttnd / = the current in absolute units. 

MagneiamoHve Force (symbol fp ) is the total niagnetizlng force deyeloped 
ta a magnetio oircvit by a coil, equals 4 r i^/, and the unit is the gil- 
heri. 

MdmUamfce, or Magnetic ReHstance (symbol (J^, is the resistance offered to 
tibe macnetle flax by the material magnetizeOf and is the ratio of magneto- 
Botireiorce to magnetic flux; that is, unit magnetomotive force will generate 
a unit of magnetic flux through unit reluctance : the unit is the oersted; i.e., 
the reluctance offered by a cubic centimeter of vacuum. 

Miaguetic J^ermeability (symbol fi) is the ratio of the magnetic indnotion 

^ to the magnetizing force JCt that is ^ = m> 

Magmetie Su8cq[ftibiUtg (symbol «) is the ratio of the Intensity of mag- 

n to the magnetizing force, or k = ;^ • 

Bdmetivit^, or SpecUic Magnetic Reeistance (symbol v), is the reluctance 
nait of_ length and of unit croes-seotton that a material offers to being 

SlectroBiagvettc ITnlta. 

RtHetanee (srmbol R) is that property of a material that opposes the flow 
«f aeurrent or electricity through it; and the unit is that resistance which, 
vifli an electro-motive force or pressure between its ends of one unit, will 
fermit the flow of a unit of current. 

nw practical unit is the oAm, and its value in C.S.O. units is 10*. The 
Litedard nnit is a column of pure mercury at 0^ C, of uniform cross-section, 
IMZ centimeters long, and 14.4521 grammes weight. For convenience in use 
I irverv high resistances the prefix meg is used; and the megokmy or million 
MBS, becomee the unit for use in expressing the insulation resistances of 
[sshmarine cables and all other high resistances. 

L MAeetro-moHve Force (symbol E) is the electric pressure which forces, the 
HBratt through a resistance, and unit £.M.F. is that pressure which will 
^hnt a nnit c^irrent one ampere through a unit resistance. The unit is the 
nltfSiHi the practical standard adopted by the international congress of elec- 
Menas at CLicago in 1893 is the Clark cell, directions for making which 
-01 be given farmer on. The E.M.F. of a Clark cell is 1.434 volt at 150 C. 

The value of the volt in C.G.S. units is 10*. For small £ Ji.F's. the unit 

UHtoU, or one-thousandth volt, is used. 

lbs International Volt is 1.1358 B. A. volts; and the ratio of B. A. volt 
die International volt is .9866. 

difcremce of Potential^ as the name indicates, is simply a difference of 

aetric preeeore between two points. The unit is the volt, 

Oerrent (symbol /) Is the intensity of the electric current that flows 
hough a clroait. A unit current will flow through a resistance of one 
;<kaL, with an tfectro-motive force of one volt between its ends. The unit 

tkeampere, and is practically represented by the current that will eleotro- 

Sa^Kwit silver at the rate of .001118 gramme per second. Its value 
. units is 10 ~*. For small values the milliampere is used, and it 
■Is one-thousandth of an ampere. 

n« QwanHiv of Electricity (symbol which passes through a given cross- 
Ktion of an individua] circuit in t seconds when a current of /amperes is 

Sis eqnal to Jt units. The unit is therefore the ampere-second. Its 
the Coulomb, and its value in C.G.S. units is 10-*. 
Cetpacity (symbol C) is the property of a material condenser for holding 
dMrae of electricity. A condenser of nnit capacity is one which will be 
wed to a potential of one volt by a <mantity of 1 coulomb. The unit is 
wad^ ita C.Q.S. value is 10-* ; and tnis being so much larger than ever 
ilna in practical work, its millionth part, or the micro-farad^ is used as 
practieal unit, and its value in absolute units is 10 ~ i^. A condenser of 
4hird micro-farad capacity is the size in most common use in the U. S. 
Ifattoi c Energy (symbol W) is represented by the work done in a circuit 
eondnetor by a current flowing through it. The unit is theJotUe, its 
lute ralne la 10'' ergs, and it reprepresents the work done by the flow 
He second of unit current (1 ampere) through 1 ohm. 
EUetrie Power (symbol F^ is measured in watte^ and Is represented by a 
of 1 ampere under a pressure of 1 volt, or 1 Joule per second. "Die 



BTHBOLS, UNITS, HEASUBEHENT3. 



hfiil 



ll 

C 1 



lit 

111 

jp 

• Is 

If 



II il II II nil II 

- t. . » &.fc ft. 



JM 



II 4 



1 

lis 

111 

m 

in 



liss 

sill 
Iffl 

Is si 
lis 



EI^tiTRICAL ENOINEKRING UNITS. 



.1! 
Ill 



Hi il 

« I » 3 4 



II 






I -I ^ 



11 

is 



Nitfljlil 

' 5 ? : 1 1 3 1 1 i- 






8 



SYMBOLS, UNITS, INSTRUMENTS. 



I 

■ 

a 

e 
Z 

n 

I 

9 

■ 

or 

£ 

4! 

1 

a 







£22s3 



88 W 



S 

a 

1 



Sao 






6 



5^( 



© 2. 



£•5 



03 



•i 



•3 

o 

I 



1. 






s 

V 

E 

.£4 
O 



o 
.d 

6 



5 13 5 






o 



i^si 



9 
O 

5 



^-"2 a 



o 






9 
0) 

B 



•S 2 



fib ••* 

® ■♦» 

•3 * 

1^ 



I 






8 S S 



Xi 






.a 



2 



» 







ff 



s. 



O ^ M 






9 

s 

s 
o 

V 

6 

I 



o 

a 



a 

9 
9 . 

.a 

08 



§ S o 
•S "S 'S 

u^ I S I 



I 



III 



*«• HN ^ 



i, ?1 t f^ 

^ ^ 2i 2, 



2j "^ "^ t^ s "^ ""J 






e^ 



II II II II ]i II II II II . II > E > 

fcjSoO^ft, o.;*, ?.s .ts II]] II 

N ^ 03 



C5 
I 



►-* •^' <-:: f" ^ *• * «r ^ 



• « ^ N ^ fl^ 




s 

9 

00 






s 





O 



c 



as 00 ^_ 

O . 9 *iO ° 9 




I 

Pi 



3 

9 



OQ 



INTSBNATIONAL BLECTBICAL UNITS. 9 

watt eoTuds 10' absolute unite, and 746 watte OQnals 1 hone-power. In elec- 
trie Seating and power the unit kilowatt, or 1000 watte, is oonslderably used 
to M,rwd the use of large numbers. 

JSoMfinfir (symbol o) is the speclfle reelstanoe of a substance, and is the 
raslstence in ohms of a centimeter cube of the material to a flow of our- 
rsnt between opposite faces. 

Qmduetance (symbol G) is that property of a metal or substance bv which 
ft eondncte an electric current, and equals the reciprocal of ite resistanoe. 
The unit proposed for conductance is the MhOt but It has not come into 
prombient use as yet. 

Qmdnclivitp (symbol v) is the specific conductance of a material, and is 
therefore the reciprocal of ite resLBtiTitT. It is often expressed in compari- 
•on with the conductivity of some standard metal such as silyer or copper, 
and is then stated as a percentage. 

Imduetance (symbol £), or coefficient of self-induction, of a circuit is that 
coefficient by which the time rate of chan^ of the current in the circuit 
most be multiplied in order to give the E.M.F. of self-induction in the 
dreait. The practical unit is the Httnry^ which equals 10^ absolute units, 
and eziste in a circuit when a current varying 1 ampere per second produces 
%wolt of electro-motive force in that circuit. As the henry is so large as to 
be seldom met with in practice, 1 thousandth of it, or the miUi-henry, is the 
SBit most In use. 

Below will be found a few rules for reducing values stated in electrostatie 
■nits to unite in the electro-magnetic system. To reduce 

eleotrostatic potenHeU to volt$, multiply by 800 ; 

** capacity to micro-faradM^ divide by 900,000 ; 

** quantity to eouUmbw, divide by 3 x 10* ; 

^ current to cunperes^ divide by 3 x 10*; 

" rtMittanee to okm$, multiply oy 9 X 10^^. 

nmMlf ATlOIf AI. SIiECTRICAI. IJlflTA. 

At the International CJongress of Eleotrioians, held at (Thicago, August 21, 
Un, the following resolutions met with unanimous approval, and being 
approved for publication by the Treasury Department ox the United States 
wrremroent, Deo. 27, 1893, and legalised by act of Congress and approved 
hj the President, July 12, 1894, are now recognised as the International 
imite of value for their respective purposes. 

RESOL VED, That the several govemmento represented by the delegates 
of the International (Congress of Electricians be, and they are hereby, 
recommended to formally adopt as legal unite of electrical measure the 
following: 

1. As a unit of reaistanee, the International ohm^ which Is based upon the 
ohm equal to 10* unite of resistanoe of the C.O.S. system of electro-magnetic 
ttoJte, and Is represented by the resistance offered to an unvarying electric 
current \^ a column of mercury at a temperature of melting ice, 14.4521 
grammes In mass, of a constant cross-sectional area, and of the length 106.3 
ccDtimeters. 

2. As a unit of current^ the International ampere, which is one-tenth of the 
imit of current of the C.G.S. system of electro-magnetic unite, and which is 
represented sufficiently well for practical use by the unvarying current 
which, when passed through a solution of nitrate of silver in water, in 
seeordance with the accompanying specification (A) deposits silver at the 
rate of 0.001118 gramme per second. 

3. As a unit of electro^motive force the international volt which is the 
E.M.F. that, steadily applied to a conductor whose resistance is one Inter- 
national ohm, will produce a current of one international ampere, and 

which is represented suffleiently well for.praotical use by ^^04 of the X:.M.F. 

between the poles or electrodes of the voltaic cell known as Clark's cell at 
a temperature of 15^ G, and prepared in the manner described in the ac- 
companying specification (B). 

4. As the unit of quantity ^ the International coulombt which is the quan- 
tity of electricity transferred by a current of one international ampere in 
one second. 

5. As the unit of capacity the international farads which is the capacity 



( 



1 



10 SYMBOLS^ UNITS, INSTBUMBNT8. 

of a oonductor charsod to AvotenHal of one tntemoHonal voU by one inter- 
national coulomb of electricity. 

6. As the unit of workf the Joule, which is 10^ unite of work in the C.O.S. 
system, and which is represented sufAdently well for practical use by the 
energy expended in one second by an international ampere in an inter- 
national ohm. 

7. As the unit ot power, the waM, which is equal to 10 ^ units of power in the 
C.G.S. system, and^whicii is represented sufnoiently well for practical use 
by the work done at the rate of one Joule per second. 

8. As the unit of induction^ the henryf which is the induction in the cir- 
cuit when the E.M.F. induced in this circuit is one international Tolt, while 
the inducing current raries at the rate of one international ampere per 
second. 

•peciflcatloM A. 

In employing the silver yoltameter to measure currents of about one 
ampere, the following arrangements shall be adopted : 

The kathode on wmoh the silrer is to be deposited shall take the form of 
a platinum bowl not less than 10 cms. in diameter, and from 4 to 5 cms. in 
depth. 

The anode shall be a disk or plate of pure silver some 30 sq. ems. in area, 
and 2 or 3 cms. in thickness. 

This shall be supported horizontally in the liquid near the top of tho 
solution by a silver rod riveted through its center. 

To prevent the disintegrated silver which is formed on the anode firom 
falling upon the kathode, the anode shall be wrapped around with pure 
Alter paper, secured at the back by suitable folding. 

The liquid shall consist of a neutral solution of pure silver nitrate, con- 
taining aoout 15 parts by weight of the nitrate to 86 parts of water. 

The resistance of the voltameter changes somewhat as the ourrent passes. 
To prevent these changes having too great an effect on the current, some 
resistance, besides that of the voltameter, should be inserted in the circuit. 
The total metallic resistance of the circuit should not be less than 10 ohms. 

Method •r maklMg- a ]Wetta«v«HseMt. — The platinum bowl is to 
be washed consecutively with nitric acid, distilled water, and absolute 
alcohol ; it is then to be dried at 160^ C, and left to oool in a desiccator. 
When cold it is to be weighed carefully. 

It is to be nearly filled with the solution, and conne<ited to the rest of the 
circuit by being placed on a clean copper support to which a binding-screw 
is attached. 

The anode is then to be immersed in the solution so as to be well covered 
bv it, and supported in that position ; the connections to the rest of the 
oirouit are then to be made. 

Contact is to be made at the key. noting the time. The ourrent is to be 
allowed to pass for not less than half an hour, and the time of breaking 
eontact observed. ^ 

The solution is now to be removed from the bowl, and the deposit washed 
with distilled water, and left to soak for at least six hours. It U then to be 
rlused successively with distilled water and absolute alcohol, and dried in a 
hot-air bath at a temperature of about 160° C. After cooling In a desiccator 
**m ^ ^J?®%^®^ Ag&in. The gain in mass gives the silver deposited. 

To find the time average of the current in amperes, this mass, expressed 
m grammes, must be divided by the number of seconds durins which thf 
ourrent has passed and by 0.001118. 

In determining the constant of an instrument bv this method the current 
«f«»^fc.^5i as nearly uniform as possible, and the readings of the instru- 
ment observed at frequent intervals of time. These observations give a 

SSIILr^i^^KT^'®^ ^\^ reading corresponding to the mean current (time 
average of the current) can be found. 

tW^readln*"* ** calculated from the voltameter resulU, corresponding to 

The current used in this experiment must be obtained from a battery and 
not from a dynamo, especially when the instrument to be calibrated Is an 
electrodynamometer. 

ftpecMlca«l«B B. — The Volt. 

The cell has for its positive electrode, mereory, and for Its negative elec- 
trode, amalgamated sine : the electrolyte oonslsts of a saturateosolution of 



BPEOIFIOATtaH ft 



11 



tfMtqhluto and merenrooa sulphate. The eleotromoilTe tone Is 1^484 Tolts 
at 15° CC, and, between 1(P C. and 25o C, by the increase of !• C. in tempera- 
mre, tlie eleetromotlTe foree decreases by .00115 of a volt. 

1. BrmpmnMmm ef the Mercmvy. — To secure purity it should be 
Int treated with acid in the usual manner, and subsequently distilled in 

TaCQO. 

S. PreparstloM ef the Zl»c Amalcan.— The sine designated in 
eoDunerce as ** commercially pure** can be used without further prepara- 
tton. For the preparation of the amalgam one part bv weight of sine Is to 
be added to nine (9) parts by weight of mercury, and ooth are to be heated 
ta a porcelain disli at 100^ 0. with moderate stirring until the zinc has been 
fully diwolved in the mercury. 

3. Prvpanatieia of tlie MeswHooe A«Ipluate. — Take mercurous 
folDlute, purchased as pure, mix with it a small quantity of pure mercury, 
aad vash the whole thoroughly with cold distilled water by agitation in a 
bottle ; drain oif the water and repeat the process at least twice. After the 
laitTashine, drain off as much of the water as possible. (For further de- 
tails of ponilcation, see Note A.) 

4. PrapanatloB of the Ziac Solpluato Aolvtloa.— Prepare a 
aeotral aatorated solution of pure re-crystallised sine sulphate, free from 
inn. by mixing distilled water with nearly twice its weight of crystals of 
pare zinc sulphate and adding zinc oxide in the proportfon of about 2 per 
ent b? weight of the zinc sulphate crystals to neutralize any free acid, ^e 
aymk should be dissolved by the aid of gentle heat, but the temperature 
to Thieb the solution is raised must not exceed 90^ C. Mercurous sulphate, 
treated as described in 3. shall be added in the proportion of about 12 per 
ecu by weight of the zinc sulphate crystals to neutralize the free zinc oxide 
laaaini]^, and then the solution filtered, while still warm, into a stock 
bottle. Crystals should form as it cools. 

i. PiepsitwtloB of the Meiwrova Sislpliato aiad Zioc ftial- 
pkale JPaete. — for making the paste, two or three parts by weight of 
Bereoroos sulphate are to be added to one by weight of mercury. If the 
fidphate be dry, it is to be mixed with a paste consisting of zinc sulphate 
o^Mb and a concentrated zinc sulphate solution, so that the whole con- 
*aaXtt a Btiif maas, which is permeated throughout by zinc sulphate crys- 
t>lt and globules of mercury. 

If the sulphate, however, be moist, only zinc sulphate crystals are to be 
>dded ; care must, however, he taken that these occur in excess, and are 
Mtdlisolved after continued standing. The mercury must, in this case 
•bo, permeate the paste in little globules. It is advantageous to crush the 
ifaK f olphate crystals before using, since the paste can then be better 
Baaipalated. 

le se« op tho Coll. —The conUining glass vessel, represented in the 
lenopanying llgnre, shall consist of two limbs closed at bottom, and Joinea 
•bore to a common neck fitted with a ffround-glass 
^^liper. The diameter of the limbs should be at 
n«t 2 ems. and their length at least 3 cms. The 
>eek should be not less than 13 cms. in diameter. 
it the bottom of each limb a platinum wire of 
^t 0.4 mm. in diameter is sealed through the 

To set up the cell, place In one limb mercurv, 
*si in the other hot liquid amalgam, containing 90 
^vta mercury and 10 partu zinc. The platinum 
vvea at the bottom must be completely covered 
b^the mercury and the amalgam respectively. On 
fte mercury, place a layer one cm. thick of the 
^ and mercurous snlphate paste described in 5. 
»th this paste and the zinc amalgam must then 
kenvered with a layer of the neutral zinc sul- 
1^ crystals one cm. thick . The whole vessel must 
■eabe filled with the saturated zinc sulphate solu- 
^ and the stopper inserted so that it shall just 
^h it, leaving, however, a small bubble to guard 
^hml breakage when the temperature rises. 

before finally inserting the glass stopper, it is to be brushed round its 
^Vper edge with a strong alcoholic solution of shellac, and pressed firmly 
* Plaoe. (For details of filling the cell see Note B.) 




Fxo 1. 



12 



SYMBOLS, UNITS, INSTRUMENTS. 



i 





• 



I? 



(4 









g§ 



A e ^< 



S S s 



'*5 



I 
^ 



h 






8 - 



I© 



5 § S 



- 1 



3S S 



5> 



P IS 



C4 «H 



8 



CO 



»-i 00 

B ::• '°- 

S 2 a 






t- 



N 

o 



04 



& 



f: r: 



w 















els 






i 



0> 






^ 



s? 









* S 



s 



eo 



1^ 









$ 



§ I I 






^ 



S o 






S 8 



I- 



i I 



* S5 9 

C» i-l t* 



s 



■as 
p « 



5 o 

0» 1»H 



00 






6 



5. 8 



•«8 






^ 






- I §, 



d 




n 



I 









& 



ill I ^ ' 



' S 



e 



ilo 






& 



s ^ 

«? 



CI 



'^ s § § 



e< 



S^ 



s 



s 






*h|& 



- 2 
s g 

5 ? 



«^ 00 S O 

s i '5. '^ 



op 






00 •-< 






00 

04 i-H 



i§ 






s 






X X 



i 



X 



^ 00 



« 



X X 






Ef 



u 



•a 
I 

e 

S ® 



9 



o &< 



hi h 

be bO 



4> 





o 
0^ 



V 



o 



a 
o 



e8 
If 



9 
» 

s 

a 
« 

e 

kl 

O 



6 

S 
ee 

hi 
to 





E. 



W S 



9 O 
4) « 












DSSCBIFTION OF INSTRUMENTS. 13 



Mmtmm tm tlM Apeeiflc«tl«Mi« 



(J}. ViM Hevcvrovs S«lph»te.—The treatment of the merouroiu 
Bolphate bM for its object the remoyal of anv mercuric sulphate which de- 
eomposes in the preeenoe of water into an acid and a basic sulphate. The 
latter is a yellow substance — turpeth mineral ^ practically insoluble in 
vster : its presence^ at any rate In moderate quantities, has no effect on the 
cell. If, however, it be formed, the acid sulphate is also formed. This is 
lolnble in water, and the acid jproduoed affects the electromotive force. The 
oblect of the washings is to dlssolTe and remove this acid sulphate, and for 
this purpose the three washings described in the specification will suffice in 
lesriy all eases. If, however, much of the turpeth mineral be formed, it 
ibows that there is agreat deal of the acid sulphate present ; and it will then 
be wiser to obtain a fresh sample of mercurous sulphate, rather than to try 
by repeated washinn to get rid of all the acid. 

The free mercury helps in the process of removing the acid ; for the acid 
■loeuric sulphate attacks it, forming mercurous sulphate. 

Pore mercurous sulphate, when quite free from acid, shows on repeated 
vMhing a faint yellow tinffo, which is due to the formation of a basic mer- 
carooB salt distinct from the turpeth mineral, or basic mercuric sulphate. 
Ike sppearanoe of this primrose yellow tinge, which is due to the formation 
of a basic mercurous salt distinct from the turpeth mineral, or basic mer- 
eurie sulpluute, may be taken as an indication that all the acid has been 
rasoved ; the washing may with advanti^e be continued until this tint 
Meara. 

(B). jnillar tlio Cell. — After thoroughly cleaning and drying the 

&B vessel, place It in a hot-water bath. Then pass through the neck of 
vessel a tnin glass tube reaching to the bottom to serve for the intro- 
dsetion of the amalgam. This tube should be as large as the slass vessel 
viU admit. It serves to protect the upper part of the cell irom being 
wiled with the amalgam. To fill in the amalgam, a clean dropping-tube 
about 10 cms. long, drawn out to a fine point, should be used. Its lower end 
k bffoosht under the surface of the amalgam heated in a porcelain dish, and 
fome of the amalgam is drawn into the tube by means of the rubber bulb. 
Ibe point is then quickly cleaned of dross with filter paper, and is passed 
throi^ the vrider tube to the bottom, and emptied by pressing the bulb. 
Tb/t point of the tube must be so fine that the amlagam will come out only 
oa iqueexing the bulb. This process is repeated until the limb contains the 
dadred quantity of the amalgam. The vessel is then removed from the 
saier-batlL. After cooling, the amalsam must adhere to the glass, and 
most show a clean surface with a metallic luster. 

For insertion of the mercury, a dropplng-tube with a long stem will be 
loond oonrenient. The paste may be poured in throuah a wide tube reachp- 
isf nearly down to the mercury and having a funnel-shaped top. If the 
piste does not run down freely it may be poshed down with a small glass 
rod. The paste and the amalgam are then both covered with the zinc sul- 
•ttate crystals before the concentrated zinc sulphate solution is poured in. 
lUs shoald be added through a small funnel, so as to leave the neck of the 
Teoel clean and dry. 

For oonrenience and security in handling, the cell may be mounted in a 
fsitable case so as to be at all times open to inspection. 

In using the cell, sudden variations of temperature should, as far as 
possible, be avoided, since the changes in electromotive force lag behind 
those of temperature. 

CHAPTER III. 

TOiscRKPnoir oi* nrftTRrMEivTA. 

Although no attempt will be made here to f ullv describe all the different 
isstmmente used in electrical testing, some of tne more important will be 
Bsmed, and the more common uses to which they may be put mentioned. 

The four essential instruments for all electrical testing of which all other 
faistrumentB are but variations, are: the battery, the galvanometer^ the 
Tt$i8taMce4>ox, and the conde^iser, and following will be found a concise 
4Meription of the more important types of each. 



14 



SYMBOLS, UNITS, INSTRUMENTS. 



PlUDHAlftir JBAimSlUJBS. 

A Voltaic Battery is a device for convertiog chemical energy directly 
iato electrical energjr. 

If a plate of chemically pure sine and a plate of copper are imm««ed in 
dilute sulphuric acid no chemical action takes place. As soon, however, 
as the sine and copper plates are connected by an dectrical conductor 
outside of the liquid a vworous chemical action is set up. the sine dis- 
solves in the add. and hydrogen is liberated on the copper plate. As lon^c 
as this action takes place an electric current passes from the sine plat« 
through the acid to uie copper plate and through the conductor back to 
the sine plate. 

The chemical action in this simple voltaic cell soon becomes weaker, 
and at the same time the intensity of the electric current diminishes and 
finally becomes aero. The diminution of activity is chiefly due to the 
accumulation of hydrogen on the copper plate, causing what is known as 
"polarization." An agent introduced into a galvanic cell to preveat 
polarization is called a "depolarizer." 

The chemical reaction of a voltaic cell is directly proportional to the 
quantity of electricity passing through it. The quantity (in grammes) of 
an element liberated or brought into combination electrolytieaUy by one 
coulomb of electridty, is called its electrochemical equivalent. (See table 
on second page of section on "Electrochemistry.") The theoretical con- 
sumption of material in a voltaic batterv doing a certain amount of work 
can be calculated from the electrochemical equivalent of the material. For 
example, in a battery doing work equivalent to one horse-power hour 

746 X 3600 X .(X)3 387 

E 

grammes of sine will be dissolved: E being the E.M.F. of the battery. 

In practice the oonsxmiption of material in a galvanic cell is larger, due 
to local action. €k>mmercial zinc always contams iron, carbon, or other 
impurities: as soon as these are exposed to the liquid, local dosed circuits 
are formed resulting in the consumption of zinc To prevent this wasteful 
action, the zinc must be amalganuited with mercury. The action of the 
mercury brings the pure zinc to the surface and in contact with the liquid. 
Amalgamated zinc is not attacked by diluted sulphuric acid. 

Zinc is amalgamated by immersing it in dilute sulphuric or hydrochlorio 
acid for a few minutes to give it a clean surface, then mercury is rubbed on 
with a head brush or cloth fixed on the end of a piece of wood. 

Primary Cells may be classified into two groups; closed circuit and open 
circuit. 

Cloeesl CtrcnK Cella. — Cells of this group must be capable of work- 
ing on a closed circuit of moderate resistance for a long period without sen- 
sible polarisation. They must, therefore, contain an effective d^>olarizer. 
The best depolarizers are copper sulphate CuSO^. strong nitric acid HNOst 
chromic acid CrOg. oxide of copper CuO, and chloride of silver AgCl. 

The following table contains data on the representative types of closed 
circuit cells. 



Name. 


-fPlate. 


Electrolyte. 


Dei)olarizer. 


— Plate. 


E.M.F. 


1 
R. 


Daniell 


Zinc 


Sulphuric Acid 


Cop. sulphate 


Copper 


1.08 


1. 


(irove 


(( 


»t ti 


Nitric Acid 


Platinum 


1.9 


.15 


B onsen 


it 


11 M 


(t «t 


Carbon 


1.8 


.2 


Peggen- 
dorff 


(t 


4< If 


Bichromate of 


t< 


2. 


.2 






Potassiura- 














Sulp. acid 








Lande 


(t 


Caustic Potash 


Copper Oxide 


Iron 


1. 


.1 


Davy 


11 


Ammonium Chloride 


Silver ChlorideiSilver 


1.1 


4.5 



The values given as electromotive force and internal resistance of 
the different types of cells are approximate only. The E.M.F. depends 
upon the purity of the materials, the concentration of the solution; the 
internal redstance, furthermore, depends upon the dimensions and general 
arrangement of the cells. 



BATTBBim. 



>^«» Clvcalt Colls. — C«Ua ol Lhii group an only luitjible (or uaa nhcn 

a ct i n g polariieT, aa tha affoct of polaruatiou can be takaa cara of durinc Uie 
intcinlg of rrn. dlber by a ilow acting depolariio' or nven vithoui any 
--'-^ — ■- '- >- ^rever, „[ the (raitat importMice that do local action 



Sam.. 


-^^■"^ 


ElMlrolyte. 




-Plate. 


E.M.F 


R. 


Gaianar 


ZlDC 


OildeotZlDCMl-ani- 
mooiac, Chloride or 


BiDoiide or 
Noae 


Caibon 
Carbon 


13 


'.i 



Tha el 



~ ~ ■.: (he » 



(11. 



"bhHstcoe," dieaolTed in wi 

kbout 8 incbn higli and 6 inchea dismcLer. The 

the middle, spread out, and set on ed£e in the 
bottoTD of Ihe cell, tbe tenniaal bdng a piece of 
ntta-percha inauiated copper wire extending up 
tliTTHV> ^a aoiulion. 

The nne ii usually cast with Bnicra spread out, 

and a book for sus^enfliuf from tbe top of the iar 

' — 1, the lamuial banc on top of tb« hook. 



is aulphale o( ooppa, or 

(•ee^.Z)iea Jaaa^c. 






from 



This U 



, tbe top of t„_ ,_.. 

crystals src plac«d in the bottom of i... ... 

tbe eoRMT, Ibe jar then being filled with water to 
joM ■Dore the "crowfoot" or liac A Ubls- 
ipDonfa] of Bulphurie add is added. A saturated 
■ololioa of eoppcr sulphate forms aroiind the cop- 
per; a rui , ikfter use, a linc sulphate solution is 
lotmod kround the side, and SokIs upon th« C(i>- 
pa BuJpbatfl solution. The line of separation bet 
■ called the bint Htu. As Ihe two eorutiooa are k 
tbor diSerfml specific gravities, the name "gravity 
This ceil does not polariie, and the E.M.T.a pra< 
- ' ■ " - a eloani drcuit. If the cirei 



■ not have work ei 



— . __,_jn forming i_ 

ins an >ppearance^ike black mud. 

Car« •# *hm tlwmwttr Csll. — For ordinarv 
pomuls of "blnestooa" per cell is usually found ] 
It is better to dean out the cell and supply new nolut 
plrnisii "BhteatOD*" orrstals shaulil not be enulli. . 
Urce BB «n egg. In good eoadilion the solulion at Ihn h- 

j,^^^, ..,_. 3: : . ,„ . 



copper dcpOBJIiog oi 

"loBlworl 
best. Whe 



' about thr« 



st»rtiny » new Mttterv ' - 
farty-eigfat hours (o lo 



LIT a layer of good 
rhis oil should be 
under •WO" F. H 

liphkie and lower the internal resislance. 



8VMUOLB, UNITS, INSTBUMKMTS. 

■astAnce of the ordiDBir ffrmTity cfiU ii 2 to 3 ohmi. dcipaidii^ 
r oooditions, nich u the nM ol platn. Ibn nttmns LucMhcr, 



Xk« CeclaMikd Cell. 

Thifl «ii1 u cin« of the moet eommimLy lued outade of tedesraphy. and up 
to the kdvent of the so-cklled dry cM wu prmcticall]' the only one in uh for 
borne uid telephone work. The eLemeDta &re uno bud carbon^ with per- 
oxide of mm gm n gee about (ha carbon plate for a depolariuD^ e^*'^^' A# 
luually oopjtrticted — for (here are maoy modififatioos of the type — the jar 
u of guvBp about 7 iDchee hi^hand 5 inchee id diameter, ot BomeumeB h^uarQ, 

loDgp ahd ie plaoed jq one corner of the jar in a solution of ^l-atnmoniao. 
The oarbon plate is placed in a jwroiu cup withiD the jar. and the apace 

olatad peroxide i^ oiaDganeiie, The nal-ammoniac aolution pasaee through 
the poroiia cup and nuiBCei» the coDteols. Tliia cell will pdariie if worked 
hard or abort dreuitad. but recuperatea quickly if left on open sircuit for 
a while. The nnitance of the I«clspch^ oell vaiiei with ila nie and oon- 
ditioo, butiasaunlly Im than one ohm. The initial ELM.F. i* about t^ 
volt. It ia dcainble not to u» loo stroac a ealutioo of aal^aimnKuiiac. ke 
eryMali will be depoeited on the >ino; and nnt to Isi theaolutioa get too 
weak, M ehlorida of linc will form on the linc: both eaaditioDi will 
materially iacreaM the internal renstance ol the cell and impair iu 
effiojenoy. nn**-™-* ^ — ■' — J: = ' — ■'- i' = * •^'~ -- 




cally pan line and a uu 
in an electrolyte paale^ 

2i' long by |' diameter wilhtli^' 



vBly used for teetJDK iiuulallr 

e element* are a plate of chen 



icted the jar ia of flas 



B Fi«. 3. The paate ia pou 
, .u«n hermetically Haled. The 
rouj^h fiber tope ^ posts thereon. 
I small sjie of the cell renders it pnasible to OOD" 

■- containinjr box is providn with a pole-chan^ 

laired. Fig. 4 shows a portable testinc batt«ry 

y of these cells complete roady for use. 

I E.M.F. of the chloride of silver cell is .fl of 



ind there is noloeml 



The elements of this cell are linc in a dilute solution of sulphuric 



BATTEKIES. 



tir*raro»te of potuh. ooe mrt ■ulphurio acid, snd nine psrta water. Dii- 
aln the bkbroiute in the watw at boiling, and when «wl add the sul- 
ftarie aisd olowly. The line pl&te ia in the form of s cone, and ia plaCKl 
■ lh> bottom at a poraiu eup inside a glau jar. The carbon plals u out- 

br anaJnination, and the cup ii filled with a dilute Mluiion of aulphurio 
•diL 1& outaida jar ii filled with the electropoin. In (hia the carbon 
pU* m immcnad. 

Tbe E.U.F. ia 2 volta, and thx intsmal |-«aiMance is about halt an ohm. 
nc iDluIion is orisioally of an orange color. When thia becoRiea bluiah in 
liM. add more cryitala. Bhould the color be notinal and the cell be weak, 
■Id (raah anlpbune acid. 



a C«U. 

thia cell (Me Fie. S) are linc and copper 01 

< a tl 

L ataried. ia held in 



it thia cell (Me Fie. S) are linc and copper oxide in a wal 
e nnaah. The pIsteB ate suspended siile by side from t' 
The copper oiide, which is plated with a thin Qlm of m 



10 SYMBOLa, UNITS, IMSTKUMEMTB. 

a tnine attuhed ta the coTsr. A 1>jar of oil U 

Ins eilU. Tbe E.M.P. !■ law, etnitlng U .ts 

era ohm for Ibe largesl cell. Verj Btrous cnr- 
renu can be taken fruiu tbls cell : for laimnc, 
tbe cell bBTlni an E.M.P. of .TS Tolt and rnlat- 
ance of JTS oliia will prodnce 30 aaiperea on 



Dtj BatMrlea 

Tai^es illghdj In 

Bur^lrtrdry cell Is madeof a Hoc tubedee Fig S) lu one element, vbieh acti 
also a« tbe containing ]ar. a wrlion cjlluder ft th« negstite elemeut, and an 

parte platter, J7 parti flour, and 2 part* water. In eoDBtructlng the cell'a 
plnngergomeirliat larger than Che oaibon element iiplacDdiD tbe mldilla of 



iJfe- 


^ 


[ 


1 



the lino Jar. ai 
place, and tbe 



on. 3 parts plaeler. 

nl le fastened to 



»n pUte. Tbe K.M.K. of the Bumler cell li 1.4 volt ; the Internal re- 
Gamer diy otll, shown fn Pig. T, oonalits of a ilao cup as the posltl*« 



up of the folium 



BATTEBISB. 

ClBik Cell.— The form i>[ celj called 
Cbrk, necific&tiDru for mAkin^ whjch 
nO be tound in tbe ehapter on udjU, 
■ tbe <Hi« adopted as tbe vtandard of 
E.11F. by tbe IntemationaJ Electrical 
Coocnaa at Chicago in 1S93. The poii- 



tai« to* and 26° C. the iiicr«» of 1° C. 
deereaaee the E.U.F. .00115 rail. 
Lalv inrestisatioos by the Phyiika-' 



Tachniache R^ichnai 
•f the E.M.F. a ' 
the eh*n^ due 



oua I 

15° C 

llw Ciark~c^ great care must be~ taken 

■Adent and from the Sot that the E.M.F. 
bci behind the letoperature ch^^ise. 
- — -—-'^■trk Ciell. — TCa. 



Fla. 8. Cailiart-Clark Standard 



the soiutioii of line eiilphalc la sal 
■ad the temperature ooelGcLent 

W«>o> CadMlaM Cell. ^ The elemente of 
ud mtKcury. the eleetrolylm b«na ■•---■• " - 

if the cadnuum sulphate crystal 



cell has the ■atue elements 

■ ■' ■ CC. ThBE.M.F. i 

"- ■ 'lheCUrlt< 



- ,- - 20* C 
y the Wesi 



I E.M J", n 
( — 20° C.)" 



^1 4^r 77'°" *H'Pi»n>- 'he mdmium iulphate , 
at ^ C. and has an il-M.F. ;^ I.OIBSS '- - - 
' ™«*'='55;- The E.M.F. renmioB con 
joesB of .0001 amp. ba passed throi«h tl 
11 han largely siipereaied the Clark Tell b. 
Its ooOBlancy and lis freedom from temp 
«r*Mpiaf of Batterj Cell*. 

D E.H.F,greftter than that of or 




nold give an E.H.F. \ ^ f 



■abof 14. 

be dnirea to obt 



Flo. 9. Battery Cells in SonH' 



20 



BYMBOLS, UNITS, INSTRUMENTS. 



terminals to positlye terminals, and neeatire to negatire, adding their onr- 
rents togetiier at the same E.M.F. as in Fig. 10 t>elow. 

If still more current strength be needed, another series of cells may he 
added, and their current added to the circoit, making three times the eorrent 
of one series. 



SERIES 1 



— -^^ -_■♦• --+ r_4- - 



- ♦ - 4- - 4- - V 




Fig. 10. Battery Cells in Multiple 

The reason for this is, that when two or more resistances are pJaeed in 
parallel or multiple, the equivalent resistance is decreased, as is shown In 
another chapter. If the resistance of one series be 10 ohms, the resistance 
of two series in multiple would be one-half of ten, or 6 ohms ; that of three 
series In parallel, one-third, or 3.33 ohms ; and of four series, 8JS ohms. 



Let 



E =. B.M.F. of a single cell, 
r = internal resistance of one cell, 
R — external resistance m a circuit. 



Then for n cells arranged in aerie^^ the current which will flow will be 
represented by the formula, 



/ = 



nE 



nr-\- R 



r-i — 



E 



If R is very small as compared with nr^ then / = - • or the current ia the 
same as that from one cell on short circuit. ** 

If, as in telegraph work, nr is very small as compared with A, then 

/= "jf * o^ ^^^ current increases in proportion to the number of cells. 

The value of r is nearly inversely proportional to the area of the plates 
when fronting each other in the liquid, and directly as their distance apart. 
Therefore, if the area of the plate is increased a times, for one cell 



/ = 



E 



aE 



- + /? 
a 



r-i-aK 



Let 



Xziz the total number of cells in the battery, 

fia = number of cells in each series. 

Tip =z number of sets or series in parallel. 



Then the internal resistance of the whole battery 

Tur 

To find the best arrangement of a given number of cells (N) to obtain a 
maximum current (/) working through an external resistance {R), make 

— = Rf or the internal resistance of the whole battery equal to R. 
ftp 

In any circuit /= -t——. :-— i and for any arrangement 

voCAi resist. 



BATTBRIES. 21 

WlMn amnged for maximam corront through a glyen external resistance Ji, 

«•= y— and np= y-^. 

To find the greatest current that can be obtained from a given number of 
eells {N ) through a given external resistance (/?>, 



2 T i2r 



Br 

To find the number of cells in series (n«) and In parallel (rip) required to 
! give a enrrent (/ ) through an external resistance (/?) and to have an efli- 
cieaey (/»). 

Efficiency F=: ^'temal work 
' Total worlc 

J*R It 



^•a'+*) %+^ 



%p 

The iatemal resistance of the whole battery is 

mr Ri\ — F) . , n,EF 

— "^ — - — = — and / :^ 

np F H 

^IR ^ It 



EF "'"~J»(1 — JO 

KEACTRIGAIi MaA«lTltIir« lITSTMinHtKirai. 

The electrical measuring instruments most used in practice are galvanom- 
rwQutanoe boxes, condensers, voltmeters, anuneters, and vratt- 
with Tariations of the same, such as millivoltmeters, milliammeters, 

CtelrsusoBs 



SLTe instruments for measuring the magnitude or direction of electric 
Kots. The term galvanometer can also be properly applied to the many 
types of indicating instruments, such as voltmeters and ammeters, where a 
needle or pointer is under the influence of some directive force, such as the 
serih'fl field, a spring, a weight, a permanent magnet, or other means, and 
is deflected from zero by the passing of an electric current through its 



Nearly all galvanometers can be separated into two classes. The first is 
the maoing-needl* class. A magnetized needle of steel is suspended with 
its axifl boriaontal so as to move freely in a horizontal plane. The suspen- 
sioa is bT means of a pivot or fiber of silk, of quartz, or of other material. 
The needle normaJly points in a north and south direction under the influence 
of the earth's magnetic field, or in the direction of some other field due to 
aojciliary magnets. Near to the needle, and frequently surrounding it, is 
plai-^ a ooil of wire whose axis is at right angles to the normal direction of 
the needle. When a current is passed through the coil the needle tends to 
torn into a new position, which lies between the direction of the original 
field and the axis of the coll. 

The second class is the moving coU or d'Arsonval class. A small coil is 
sespended by means of a fine wire between the poles of a magnet. Its axis 
te normally at right angles with the lines of tne field. Current is led into 
Che eofl by means of the suspension wire, and leaves the coil by a flexible 
wire attached underneath it. 

Tbe /Iffttre of merit of a galvanometer is (a) the current strength required 
to eaiwe a deflection of one scale division ; or (6) it is the resistance that 
mnst be Introduced into the circuit that one volt may cause a deflection of 
dlTlsion. This expression for the delicacy of a galvanometer is 



U:<1TS, IN8TKUMENT3. 



InanlDcletit aiilcas tbe following quuitltfsa sr« sIbo elien : the Teeislwicf 
ol the VHlTBiionieter. the dtiitaiica of tli« scale from the mirror, tha Bi>e ul 
tbe Bufe dirlsluiia, and the Mms of vibration tl Ibe needle. 

The lemitiveneti of a gftlvnnometor is the dlSerence ot poMntUl necea. 
B*^ to be LmpreMed betweea tbe aalTuioiiaeter tensLiuJt In order to pro 
dace adeSectlon ot one scale dlvisiun. 

Movlsr*!'***"* ValvaaoBicters. ] 

<a.) The Tangm Galra«omtttT. II the inside diameler of tbe coll vhieb j 
■ arrounda a needle, held at lero by the earth's Held, be at least 32 times ttia ' 
length of ilie ueedle, then the deflectioni uf the needle which coireepODd to 
different eurrent streuglha sent throiuh the colls, will be sncli tbnt the 
current strengths will vary directly u the tnugenls of the angles o( defleo- 

merlvmnch i»nl (or tlin nhiuiliiie uieasnremenl olourrent. IlhBE,howoTer, 
of which are of uncertain magnitude; and. 



rmore, for accuracy in [he reaalls yielded by It 
tism. 1 
rvlcinUy. 



eiacl Ln^ivrledso of the lalue of the borlionta] component of the earth's 
magnetism. Tills Quantity la condDually changing, and is atTected much 
by the presenee ot large massn of iron and the eilstence of Leary cnrrenta 



nsofa tangent galvanometer coll. In cen 

iber of turns In the coll, 

lortiil intensity of the earths magnetism, 

ml Bowing In the coll [o absolute units, and 



. Tftugeut UalyanomeU 





oneformofthLlnal. 


nrasnt. Tbs 


rti rod to the cente 


of which 1. 


> lbs plane ot tbe m 




oneendoftheqiuvrt 


tube, l" fu- 


tened a oomplei uF 


Si'SC. 


lectad mlnato tniMn 


loae needles 


&11 point §D tbs u 
At the other end o 


tba quarta 


(nbelntaslsDedaalni 


ilar complex 


with the polarity rev 


tbs too sompleiei 
equal magnetfe mo 




"thS'^'r^th"; 


fleld.nodlrootlfsM 


on woDld be 


felt. In fact, thli a 


Btion IB lory 




alion form. 


vhal i< called an utaHc BVB ten). 


Each magnetlo co 
eloeed b«tveen tw 


"^wSe col>" 


ThefourcollBaiea 




bInding-poBte. go as 








Current i» lent thn 


ugh them In 


the proper illrsction 




ineaehea«edsHectl 




wSw no""BU.tlc' 




fatlgne and 


which la vsrj atron 


K, i> used as 




adju«tnble 




on tbe top ol 


M-Hi'. 


fl,—,S 


earth's fleld chu be 




any extent. Under 




»Te force Che sens 




oHslllBt^nof iheiie< 


XfiS:: 


long. Tbe limit of 
la largely InBucncc 


by tbe pa- 



Hecclom of tbe nsedle are ob- 

and scale. Flg.'tSahDWH^BUehTn 

reflecta an iraage of the scale Into 
Che objective of Che teleacope. 
ContlnnouB worli with Ibe teV 
Inly Cire«ome. Where much gal- 
ne pereon, a ray of lliht from a 
!ted as to be refleetetT from the 
Such a lamp and scale la ahown 
ulckly to reat when uoder tbs In- 



r 

24 STHBOLH, tnriTS, IN8TBOMBMT8. 



lKiuilncLo««d chnxnlHr i 

>Hdlal« Ineloced In & bniioT niiuig in ■ oiocE oi 

Uoced bj the iDOTliig needle reftct upon It and 

^B«t ofdelloney U required. In Ihe moal Mm 
•ftbeaoll. Thiai 



QALVAHOUBTERS. 26 

me nifllhod of dunpEng mnat b« emploved. OlM 

« vuB u iba moving syitem. and kllow It to iwlnt 



Via. U. 

km o4 gmlTUioDieler hu Ihs /olloirrng icood pcdnta : lt« rendlngn ace bnt 
tiftatlv klf«ct«d bj the proaenca ot raMaatt\c subetuim in tlie Tirlnlty, uid 
npnctlcsllTiodependeiiCoflbeeartb-ineld; Ibslai'trumfltit cm b«eBallT 
mU d«Bd-bsm(; nnd many farmi ars not mucb nlfpcted by ilbcHtloDB. 

B. U ahowi • f arm of D'Ationvsl galTnnumeter of blah wtiiilbirity, Tbe 
(ibavD It tbe Hgbt) u iticloasdlii an alumlDuin lubo. Eridy cutreuta 
''re iDdoead In tbia tube wben tbe cnll ^wingK. Tb?y Fnuae damping, Knd, 
«k ■ pn^wr Ihlckneaa of tabe, Ebe gyitam may ba made apsrlodlc. 



Bklltatia ^[vftoomelen are used for measurmg or cam 
lectrietty such a< flow in drcuite when a ccinJenser ii 
cue aux linkacea are disturbed. The time of osrilli 



iwn Sl'tbe°nJIi3K 



SYMBOLS, UNITS, IKSTBUHENTR. 



All c&lyBnonMiun ha' 



be Ions ms emnpanil with ihn di 
iping or the nccdJe the eiuuititii 
if half ths ugla of the fin 
dumpinc. The rom 
le with BaLvLDamftei 



Tuter, by E. L. Nicbols.) 



of m«iuu for MsiLy 



bj m. r. Mortkrap. 

(Abntraot from Tnnn. A. I. E. E.) 
. hae dmrribed was devBloped to meat the frequent need 
ud AccuTfttfily cv1ibrH.tiDg »]temiLtiDff-curr«it imitrit 
voltmeten, irh&t?rer thor o&pacity. 






ivfliiMB, and btnnp porfaotly *'i 
with them it hoa an 



le operatioD of Uie inaUU' 



^. ^^ 



mail dqwndj upon the heating t 

RererrinE to Fig. IS, two emsll 
wire whBD shunlH are used, lie 
0.158 in., beiDE held near their ei 

medium ot heavy lesde and ■oI<lei 

One faee of a email cirmlar die 

St their middle point, a 0.5-in. ci 




of ivory. D, 
™lar mirror 



being fastened to t> 



QALVANOMKTEBS. 27 

bca. Futcned >t the oeatEr of the ivory dink aad half ny bctmen lb* 
warn. nbtD tha dulc ia id poution an tlio vim, is a xmall hook. To this, 
tbougb the maliuin of a (hrwd. u futroeda imaJI ad J lu table spiral ■prins. 
The small iTory disk malDtains iu posilioD by frictioa aad the leasion of 
the sprins. Tho wires bend hack under Ihf tenaion of the apiing about 
0^75 InTTrom the vertical. The ivory diak does not rent directly upon the 
wirei but b^rs upon Okch win through the medium of a stoall agate stud 
shaped like the hwi of a screw, each wire beiDg in the slot of the agate alud 
which nets upon it. 

Tub two iroiy damps holding the wires oeiu- their upper extremity are 
made sepaimtely sdjuatsble in a vertical 
direction by meana of thumbecrews which 
pais through the hard-rubber top of the 
mnmment. Springs • « preveat lost motion 

doS. ' '""^ "** "" """^ "" " 

The airannment of psrta above described 
ii supported by a brass frame aud a circular 
kaid-nibber top. This frame dropa into a 
circular nickel -plated brass case (Fig. 17). 
Ihe cue has a window in il directly in 
faonl of the mirror on the smalt ivory disk. 
Tig. 17 ihowi dearly Ihe arrangemant of 
parts and Ihe appearance of the mstrument. 

By means of the adjusting screws the 
tension of the iwu wires may be so adjusted 
(hat the plane of the mirror will be vertical 

SHing which holds the mirror aeaiost the 
wires. Nov if any dongation occurs in the 
■ire on the tifihl, that side of the mirror 
will be drawn downer back by thesprii^, or 
a deflection to the right is obtained. Oke- 
wisc if an oJoORation takes place in the wire 
on Ihe left, the mirror will deflect to the left. 
II, howevir, an exactly equal dongation Fio. 17. 

plane of the mirror will not tilt but simply move back keeping psrallel to 

If the mirror is obsirved with a tdescope and scale, say at a distance of 
one mettr, very minute angular defiectioos of the mirror will be easily 
observed, while a sinking back of the plane of t)ie mirror away from Ihe 
sale will not be obeervable. 

Now if an alternating current of unknown streogth be sent Through the 
•ire A. the wire will e&ngate, deflecting the mirror toward the left. Pass 

mtil Ihe deflection is reversed and brought back to lero on the scale. If 
vhen the deflection is lero. and certain precautions to be staled later have 
deal obeerred, the strength of the direct current is known. Ihe strenglh of 
the alleniating currenl will also be known; for it is exactly equal to the 
dimt current. This, howevs. is on the assumption that equal currents 
throiyh the wirea A and B produce equal donKalinns of the wirra. I're- 

'' Brough the circuit : it under theee 

,. all, or only slightly, it provea th ..... 

y elougated by the same currnit strength. The I 

"Tf'ihii; 

eiwth of „ 

adjustable and measured dire 

naling current for the pitrpose o 



be not deflecled at all, or only slightfy, it provea that ihe 

practically equally elougated by the si — '■■ 

this possible email deflection 



diagram. W* and W4 reprc* 



ahuDt, preferably of mangaain, having 



28 



SYMBOLS, UNITS, IN8TEUMENT8. 



a negligible temperature coefficient, furnished with tap-off pointa c andd, 
between which the resistance R has previously been determined. The 
ammeter indicated in the diagram wiU measure from one to two amp«r<M 
of direct current; r, is a slide wire resistance along which a slider p may be 
moved, thereby varying the pressure difference at o-o from sero to ine 
value of the electromotive force of the storage battery- .* u — . i-^^- 

The pointa a, b, on the direct-current side of t*^«_«»^*J.^,T5«l!SJ 
attached to them which go «ther to an accurately cahbrated direct-current 
laboratory standard voltmeter, or to a potentiometer. 




Mwem 

POTtNTIOMITIII 



MTIMATINO- BURMNT tlM S DmECT-CUMUMT MM. 



Fig 18. 



When the instrument is installed, a permanent adjustment of the 
sistancee at any convenient temperature of the wires and leads must be 
made as follows: (see Fig. 18.) 

The resistances, 9 td 10 = 7 to 8, 

inorwwwMi*, ' 10 to 1 + 9 to 6 = 8 to 4 + 7 to 2 and 

2toc + 4tod = 3toa-h6to6. 

Thus while this gives the over-all resistance from a through the wire W^ 
to b equal to the over-all resistance from d through the wire Wm to c, the 
different portions of the circuit must be matched in resistance as stated 

* When the switch S is closed on the alternating-current aide the two 
wires Wm and Wd are thrown in parallel, and the two parallel-connected 
circuits have the same resistance, by construction, and that to th«e par- 
allel circuits at the points 2 and 4 is apphed the same potential difference, 
this potential difference being the drop on the low resistance R carrying 
the alternating current. The drop over R, inasmuch as it is a low resis- 
tance, is only slightly lowered by being shunted by the two wires of the 
instrument and their leads, and this lowering of the potential is not apore- 
eiablv greater when the two wires in parallel shunt the resistance R than 
when only one wire with its leads shunts the resistance. Disregarding 
the slight lowering of the potential, both wires will now have passing through 
them equal currents, each current being nearly the same a« would pass 
through the one wire Wa if the switch S were open, and only this wire could 

"^With^he resistances of the parallel circuits correctly adjusted to equality, 
both wires will get equal currents, both will elongate equally or very nearly 
TO and the mirror m instead of rotating will move back, maintaining ita 
Skne narallel to the position which it has with no current passing. 
"^ When Oie switch Sis thrown to the direct-current side, the potential 
drop over the resistance R is now applied to ^^e wire f^- only; and tj^^^^ 
potential difference between the points o and 6 is applied to the wure W^ 



OALVANOHXTBBA. 29 

uid b eui be Tkriad by the ■Udo' p aod ammr«d by 
-.: .^ ■pplisd at a, b. Tbe aDimMer livca Iba 

Tba ahuDt rMiataaw R nuy b« dcaisD«d to carry any ourrsDt, howsvv 
lai^ Tha niiH nauMnce K, or a oombinatloii of lenaiaactB, niay be 
densmd with aaml tap-off or potential iioiDts. k that the inaCrument 
attj slway* have approximately tbe same poleolial applied to itg alier- 
natinC^urreat aide, whaterfr tbe atrcDglb ol the current to be meaaured. 
Tbie potential drop la beat made between 0.2fi and 0^ volt. Tba necee- 
tmrj drop of poleotial bcuif ao to*, tbe eoercy djsaipated in the ahiiDU 
ia •mail, and thereton thcv may be of very moderaM tla». It ki alto euy 
to laakB them prmotietUly luui-iDdDetive^ 

OKlvsHaBantev •>>!*( B*xaa. 
II I* nften dealr«bl* to nae a iialvjuiameter ol high gentlbllltT for work 
ilwBiiaillin a mach lower unalbiniy. Again, it may be conienlent to oall- 



°^: 



1. Es;;:%r 

_— AAAAAA 1 CoDTentencB dt 

"''''*'' Die ratios be 



lOD, and 1000 ; that ia i, A. or .1,, 
t to go throuffh the galvanometer wblle 
■buDC. lnfT(.l*let 



al eorrent flowing In the drcalt. and 

rt flowing thrDagb tbe galvaoometer, 

= g- + I = tbe MaUiplymg potcrr of tbe •boDt. 

nlwUch will give a certain multiplying power, h, la 

aqoal to ^^^1 ■ Fig. » abovi a form 

o( ahnnt need with a galvanometer, al- 

tboBch it la perfectly teaalble to oM an 

ordlnarr realatauoe box tor the poipoae. i 

Hewn, Ayrton & Mather have developed I 

anew ihunt, which can bt uaed witb any < 

gatraitometer Ineapective of Ita reaiit- 

anee : following li a dlagrmu of It. 
A and D are termlnala for tbe galvano- 

golng and outeolng terminal! for battery 
clrCDit. To abort olrouit G, place pluga 
In j and f. To throw all tba current 
thronch G, put a ping In t only. To lue 
Ibe (honte, place a plug In b, and leave It 
thereaDtilthrDngbiuing. Inthiimelhod 

o( eitber" O or r. Tb^abunt ^i can 
therefore be uied with auy galvanometer. 

Tetnpeirature varlatlone make no differ- ~ 

•nee, provided thev do not take place Pio. 20. 

dnring one eet of teau. The reelitaiics 

r may be auy number of ohiff, but In order nnt to decreue the •enalblllt)' 

too Dneh r abould be at leaat aa large aa Q. The rnaiatance r ia divided tor 

IH* aa followa : permanemt attaebments to tbe various blocks are made at 

point) In the eoll oorretponding with ^^ j^ r^ obmt. 



MBOLS, UNITS, INSTRUMKNTS. 




-^ |/WVW, 



AyrtOQ A M&ther's Univcml Shunt. 
PRACnCAl. •TAHDABUB OF RKSISVAVCB. 



Conduct^™"). Flatipoid is 
ItsntUnl. of v«rioiu> conveni 



«,.th 




ted by Ibe rai>- 


umno 


mercury 106.3 pro. long 














hcrefore Becondary stn 


dards 




rdi»J 


will, a great dfKftw o 






nude 
»nd o 


of wire. The iriitoria 
f resLstivily. mini hav 


> aTr 


poaHn perma- 

all temperature 


ty, m 


luit liave . smaJI then: 


OD-elec 






lOuldhavearBirlyliich 
xaa bU nf Iheie quali 


n (MH 


^iCS^ 


po!d" 


^^hio f'-«l^^^)'j__'^v -f^" 


.sn:'Si-^°.' 


I It*™ 


adopted by lh«Ph™ka 
y law raittancM havm 


i,chR 




For ve 


B'Wb 





BE8I8TAKCE8. 



31 



^ 



in T»IuM of .01, .001 and .0001 ohm. the redBtanoes beinc that between 
toe two amall binding posts called the potential terminala. 



The farm of reeietanoe box most frequently met with is some type of 

wjeatstone's bridge," the theory of which U described elsewhere. 

The ooils are usually of silk insulated wire wound non-inductivelv on 
ipoob, with the ends attached to brass blocks, so arranged that brass 
phigB can be inserted in a hole between two blocks, thus short-circuiting 
the reostanoe of the particular bobbin over which the plug is placed. By 
Qoo-iodu^ye winding is meant that the wire is first doubled, then the 
dosed end is placed on the bobbin and the wire wound double about the 
bobbin. By this method any electro- 
BBipetie action in one wire is neu- 
trahsed by an equivalent action in the 
other, and there is no inductive effect 
when the circuit is opened or dosed. 

The ixMt-office pattern of Wheatetone 
brifbe is one of the most commonly 
osed, a diagram of ite connections being 
down in Fig. 24. 

Ooe arm of the bridge has separate 
reoftances of the following values: 
1,2.3. 4. 10. 20. 30. 40, 100, 200. 300, 
«0. 1000, 2000, 3000, and 4000 ohms. 
AiMtherarm is left open for the unknown 
reristance. z. which is to be measured. 
The remaining two arms each have three 
nantance coils of 10, 100, and 1000 ohms 
wroeetively. Two keys are supplied 
vith the P.O. bridge, one for dosing the 
battery drcuit, and the other for dosing 
the galvanometer drcUit. The battery 
key should be closed first; and in some 





Flo. 26. Diagram of Anthony Bridge. 



32 



SYMBOLS, UKIT8, IKSTBUHSKT8. 



i 



inBtnimentB the two keys are arranged with the battery key on top of 

the galvanometer key, ao that but one finger and one pressure are necessary. 

Prof. Anthony hais devised a resistance box in which there are 10 one 

ohm ooils, 10 tens, 10 hundreds, and 10 thousands. Any number of any 

TBM .lUT* «K>up can be connected either in series or in 

TENS UMTS multiple. The means of accomplishing this 

^w^ Xf'^L- *™ •**'' clearly in the cut. 

irc5* 

]>«ca4e Methods. 

The Wheatstone brid^ arrangement has 
the disadvantage of requiring a large number 
of plugs to short-circmt the resistances not 
in use. which introduces an element of uncer- 
tainty as to resistance of the plug eontacts 
and the necessity of adding up the values of 
all the unplugged resistances in order to deto-- 
mine the value. 
7 So ^^S- 26 shows the Weston arrangement of 

Sr 91 coils requiring but one plug per decade and a 
small number of coils. 

In a later decade arrangement by Leeds ft 
Northrup, 1, 3, 3', and 2 ohm boils are con- 
nected in series as shown in Fig. 27. 

Let the terminal of the 1 ohm coil and the 
2 ohm coil and the points of union of the 




Fio. 26. Decade Resist- 
ance Box. 



coils be numbered (1), (2), (3), (4), (5) as shown in Fig. 27. The current 
(1) and leaves the coils at the point (5) traversing 1, 3. 3'. 
2 = ohxns in all. If this series is multiplied 



enters at point 



1 (i; 
AAAAAAAA/W— + 



C2)i 3 

VVVVWVV\4 



by any factor n, then n (1 + 3 -f 3' + 2) =rn 
ohms. It will be seen that if the points 
(1) and (5) are connected all the coils are 
short-circuited and that the current will traverse 
sero resistance. If the points (2) and (5) are 
connected the 3, 8^, and 2 ohm will be short- 
circuited and the current will traverse 1 ohm. 
By extending this process so that we connect 
two and only two points at a time, it is possible 
to obtain the regular succession of values 
n (0. 1. 2, 3. 4. 6, 6, 7, 8, 9) the last value 
being obtained when no points are connected. 
The following table shows the points which 
must be connected to obtain each of the above 
values and the coils which will be in circuit for giving each value: 



3' 



(41 



C3) 



(5) 
Fio. 27. 



Value. 

= 

1 = 

2 = 

3 = 

4 = 
6 = 

6 = 

7 = 

8 = 

9 = 



Points Connected. 

(6-1) 
(2-5) 
(4-1) 

[l-t] 

(1-3) 
(2-3) 
(5-4) 
(1-2) 
(0) 



CoUsUsed 





1 


2 


1.2 


1.3 


3', 2 


1, 3', 2 


1, 3. 3' 


3, 3', 2 


1, 3. 3'. 2 



Fig. 28 shows a method of connecting these points two at a time with the 
use of a single plug. 

The circles in the diagram represent two rows of ten brass blocks each. 
To the first two blocks at the top of the rows, the points 5 and 1 of dia- 
gram 3 are connected, to the second two points 2 and 5 are connected and 



RHX08TATS. 33 

» OB, DO pointa bcins oonnectad at tba Inat PBir of bUwkK. It ia «vid(cit 
tbat i( s. idue b« LiuerUd betwem the blocks 1 and iS, ibe poiuW 1 stul 6 
of dialcrun 3 &rfl connected ^riog the vulue 0; if between the btocki 2 AOd 
5» the pointB 2 mnd 5 aie ooaueoted Eiviag tbe TaLue 1, 
•ad ao on. The vklue 9 is obtaiDRT when the plu( ii 
diapoaad of by beans ioasrteil in the laat ptii of blooka 



Id tartins dyoanua and other dactrioal apparstiu 
prodqeiD|c }MTgn aiz»unta of enarn', it ia nBoeflavy to 
UTO rtBiataacea of a capacity Humdebt t^ absorb the 
efiern dsrelo[ied. and thii ia almost invariably done 
br iba uaa ol the watbs anEoerAT. wbicH in ita 
MUpleat EarEaT eDnaiata of a box or barreJ of wood, in 
wiiieh are placed two matal eleetroda Hhiebcsti tw 
adjuatai in nlation to each other ao as to increaaa 




er aod horiaonULl aleotnxiea, 
(b) aama jar aod (daetrodee u above, 
nUr uaed; 11 ampereB.Tvo]ta, electrodeeZ] 
tan nM to 122>T. and wag slowly rinng i 

(e) Wooden trough '42* X «' X 8', vertioal sheet iron electrodes; oroeB 
■eetHin of liquid, U iq. in. Witb 10% solutioo of salt water, and lOampens 
flowing, temperature at end of run 85° F. Electrodes 411' apart, P. D. 
X> Tolta, Current deneity, about 1 amp. per eq. in.; watta aosorbad, .11 
watt per cu. in., would probably larry 13 to 15 amperee safely. 

It u appaiAnt that salt increases the ourrent canning opacity, but 
deerrasea watts abaoriied per cu. in. 

(d) WUaka)' barrel filled irith clear watar, Eleotrodat were boriioatal 
drcaW inm platea A' thiek. Plataa 20|' apart, P. D. of 486 volta gave 
e«KTBit of 2^ amperea. With platea I* apart, P. D. of 2ZS volt« cave 
3G,5 ampena at tha tnd of one hour. When temperature of the watar had 
n»ebed 179° F., much taa was civeo off. Current density ,12 amp. pet 
aq. in., and watts absorbed 30Ji per cu. Id. 

iVith laiie current dauaity aiid dir«t currait there is much deoompo- 

trodca are not to bo nooDUaanded uulees a large niunber of liol« are drilled 
throDcli tha top plate to allow escape of as. It Is seldom neoeaaary to 
nae Mronfer nhitioD than 2 or 3 per cent of salt, and in adding salt to tha 
rheostat It.ia beat to dissolve it thoroughly in a separate Tseeel and then 
add to the liquid aa needs). Liqind rheostats seem tn be mare satisfas- 



BD decompaailion of alectrodn ti 
RaaaHs ar« based upon a volum 



34 



SYMBOLS, UNITS, INSTRUMENTS. 



Water and DiluU Sulpkurie Acid. 


Water and Common Table SaU, 


Per Cent Acid 


Resistance in 


Per Cent 


Resistance in 


by Weight. 


Ohms. 


Salt 


Ohms. 


.174 


4.12 


by Weight. 




.435 


1.75 


.23 


7.84 


.724 


I.IQ 


.46 


4.65 


.986 


.85 


.70 


3.12 






.93 


2.38 






1.16 


1.90 






1.39 


1.48 



Use of salt solution is cheap and convenient, but very untrustworthy 
for accurate work. 

For the sake of convenience in choosing proper sises and loigtha of 
iron wire for submerged rheostats, the accompanying table is given. The 
safe carrying capacities are the currents the wires can safelV stand for a 
continuous run. If the apparatus is to be used for short p^ods, as in the 
case of a starting rheostat for a large motor, these values may be doubled. 

Water should be kept circulating through the barrel, enough water being 
used to keep the temperature below 200^ F. 



of Oalvaalaetl Iron ITlre. 
niieoiktialrii. 



For SabMoiiped 



Wire 


c^ # 


Minimum Length in Feet for Safe carrying 




Num- 


Safe 

• 


Capacity at Different Voltages. 


T9 A 


1 ,_ . 


carrymg 
Capacity ; 






Feet per 
Ohm, not. 


bers: 
Gauge. 










Amperes. 


100 


110 


220 


500 




20 


36 


22.8 


25 


50 


114 


8.5 


19 


42 


24.6 


27 


54 


123 


10.4 


18 


50 


26.4 


29 


58 


132 


13.5 


17 


60 


27.2 


30 


60 


136 


17.1 


16 


71 


29.0 


32 


64 


145 


21.6 


15 


88 


31.0 


34 


68 


155 


27.2 


14 


103 


32.7 


36 


72 


164 


34.2 


13 


122 


34.5 


38 


76 


173 


43.2 


12 


146 


36.4 


40 


80 


182 


64.3 


11 


173 


38.2 


42 


84 


191 


68.6 


10 


205 


41.0 


45 


90 


205 


86.5 


9 


245 


42.8 


47 


94 


214 


109.1 


8 


293 


46.9 


52 


103 


235 


137.5 


7 


347 


60.1 


55 


no 


250 


173.5 


6 


412 


53.1 


59 


117 


266 


219.0 


5 


489 


56.4 


62 


124 


J?82 


276.0 


4 


584 


59.5 


66 


131 


298 


348.0 



CONDENSERS. 



S5 



If one terminal of a source of E.M.F. be connected to a oonduotor» 
and the other terminal be connected to another conductor adjacent to the 
first but insulated from it, it will be found that the two conductors exhibit 
a capacity for abs>orbing a charge of electricity that is somewhat analo- 
gous to the filling of a pipe with water before a pressure can be exerted. 
The ehaiige will remain in the conductors after the removal of the touroe 
of supply. This capacity of the conductors to hold under a given E.M.F. a 
cfaarge of electricity is governed by the amount of surface exposed, by 
the nearness of the surfaces to each other, by the quality of the msulating 
material, and by the degree of insulation from each other. If the ter- 
minals of a battery be connected through a battery and sensitive gal- 
vanometer to a long submarine cable conductor and to the earth, it will tie 
found that a verv considerable time will elapse before the needle will settle 
down to a steady point. Tliis shows that the cable insulation has been 
ftiied with elc(:tricity; and it is common in so measuring the insulation 
resistance of a cable to assume a standard length of time, generally 
three minutes, during which time such electrification shall take place. 

A condenser is an arrangement of metallic plates and insulation so made 
ap that it will take a standard charge of electricity at a certain pressure. 
Toe energy represented by the charge seems to be stored up in the insu- 
lation between the conducting plates m the form of a stress. This property 
of insulating materials to take on a charge of static electricity is known as 
inductive capacity, and the following table shows the specific inductive 
eapacitiea of^ different substances. 

Specific liidactlT« Ciapaclty of Oiaaea. 

(From Smithsonian Physical Tables.) 

With the exception of the re8ult« given by Ayrton and Pebrt, 
for which no tempebature record has been found, the 
values are for 0° c. and 760 m.m. pressure. 



Gas. 



.4ir 

Air 



Air 



r«Tbon disulphide 

Carbon dioxide, COg 

r&rbon dioxide, CO« 

CarboQ dioxide, CO* 

Carbon monoxide, CO .... 
Carbon monoxide, CO .... 
Coal gaa (illuminating) .... 

Hydrogen 

Hydrogen 

Hydrogen 

Ni'troua oxide, N^O 

Hitroua oxide, N«0 

Sulphur dioxide 

Sulphur dioxide 

Vaeaum 5 mm. pressure . . . 
VaeuunaO.001 nun. pressure about 

Vacuum 

Vaeaum 



Sp. Ind. Cap. 



Vacuum 
= 1. 



1.0015 

1.00059 

1 .00059 

1.0029 

1.0023 

1.00098 

1.00095 

1.00009 

1.00069 

1.0019 

1.0013 

1.00026 

1.00026 

1.00116 

1.00090 

1 .0052 

1.00955 

1.0000 

1.0000 

1.0000 

1.0000 



Air=l. 



1.0000 

1.0000 

1.0000 

1.0023 

1.0008 

1 .00039 

1 .00036 

1.00010 

1.00010 

1.0004 

0.9998 

0.99967 

0.99967 

1.00057 

1.00040 

1.0037 

1.00896 

0.9985 

0.94 

0.99941 

0.99941 



Authority. 



Ayrton and Perry. 

Klemencic. 

Boltzmann. 

Klemencic. 

Ayrton and Perry. 

Klemencic. 

Boltzmann. 

Klemencic. 

Boltzmann. 

Ayrton and Perry. 

Ayrton and Perry. 

Klemencic. 

Boltzmann. 

Klemencic. 

Boltzmann. 

Ayrton and Perry. 

Klemencic. 

AjTton and Perry. 

Ayrton and Perry. 

Klemencic. 

Boltzmann. 



36 



SYMBOLS, UNITS, INSTRUMENTS. 



Bpmmmm Indvctfre Cmp^uAtj of AolMa (Air Vaity). 



Substance. 



Oaloflpar parallel to axis . . . 
Oalospar perpendicular to axis 
Caoutchouc ..... 
Caoutchouc, vulcanised 
Celluvert, hard gray 
Celluvert, hard red , 
Celluvert, hard black 
Celluvert, soft red . 
Elbonite . 
Ebonite . 
Ebonite . 
Ebonite . 
Ebonite . 
Ebonite . 
Ebonite . 

Fluor spar 

Fluor spar 

Glass,* density 2.5 to 4.5 . 

Double extra dense flint, den- 
sity 4.5 

Dense flint, density 3.66 

Light flint, density 3.20 

Very light flint, density 2.87 

Hard crown, density 2.485 

Plate, density 

Mirror . • 

Mirror . • 

Mirror . • 

Mirror . . 

Plate . . 

Plate . . 

Plate . . 

Guttapercha 

Gypsum . 

Mica . . 

Mica . . 

Mica . . 

Mica . . 

Mica . . 

Papa% dry 

Paraffin . 

Paraffin . 

Paraffin . 

Paraffin, quickly cooled trans- 
lucent. 

Paraffin, slowly cooled white . 

Paraffin 

Paraffin 

Paraffin fluid, pasty 

Paraffin, solid 



Sp.Ind.Gap. 



7.6 
7.7 
2.12-2.34 
2.60-2.94 
1.19 
1.44 
1.89 
2.66 
2.08 
3.15-3.48 
2.21-2.76 
2.72 
2.56 
2.86 
1.9 

6.7 
6.8 
5-10 
9.90 

7.38 
6.70 
6.61 
6.96 
8.45 
5.8-6.34 
6.46-7.57 

6.88 
6.44-7.46 
3.31-4.12 
7.5 
6.10 

O •«)' '4 .17 

6.33 
6.64 
8.00 
7.98 

5.66-5.97 
4.6 

1.25-1.75 
2.32 
1.98 
2.29 

1.68-1.92 

1.85-2.47 

2.18 
1.96-2.29 
1.98-2.08 
1.95 



Authority. 



Ronuch and Nowak. 
Romich and Nowak. 
Schiller. 
SchUler. 
Elsas. 
Elsas. 
Elsas. 
Elsas. 
Rosettl. 
Boltimann. 
Schiller. 
Winkelmann. 
Wullner. 
Elsas. 

Thomson (from Herts's vi- 
brations). 
Romich and Nowak. 
Curie. 
Various. 
Hopkinson. 

Hopkinson. 

Hopkinson. 

Hopkinson. 

Hopkinson. 

Hopkinson. 

Schiller. 

Winkelmann. 

Donle. 

Elsas. 

Schiller. 

Romich and Nowak. 

Wullner. 

Subnuuine cable data. 

Curie. 

Klemencic. 

Curie. 

Bouty. 

Elsas. 

Romich and Nowak. 

Abbott. 

Boltimann. 

Gibson and Barclay. 

Hopkinson. 

ScluUer. t 

Schiller. 
Winkelmann. 
Donle, Wullner. 
Axons and Rubens. 
Axons and Rubens. 



* The values here quoted apply when the duration of charge lies bet w ee n 
0.25 and 0.00005 of a second. J. J. Thomson has obtainea the value 2.7 
when the duration of the charge is about A X 10* of a second; and this is 
confirmed by Blondlpt, who obtained for a similar duration 2.8. 

t llie lower values were obtained by electric oscillations of duration of 
charge about 0.00006 second. The larger values were obtained when 
duration of charge was about 0.02 second. 



1 



C0NDEN8BR8. 



37 



■pMlfle Iiid«c*lve Capocttj of Solids (Air 'WJmlktj). — Oont. 



Substance. 


Sp.Ind.Cap. 


Authority. 


Poredain 


4.38 
4.55 
4 ^ 

2.48^2.67 

18.0 

5.85 

10.2 

3.10 

3.67 

2.96-3.73 
2.18 
2.25 

3.84-3.90 

2.88-3.21 
2.24 
2.94 


Curie. 


Quartx, along the optic axis 

wrti, tranar^ve 

Resin 

Rock salt 


Curie. 

Curie. 

Boltsmann. 

Hopkinaon. 

Curie. 


Rock salt 


Miminin . . ^ 


Rrktninh Anrl Nowak. 


Shellac 

Shdlae 

fteflac 

Spermaceti 

Spermaoeti 

Sdphur 

Sulphur 

Solphur 


Winkelmann. 

Donle. 

Wullner. 

Rosetti. 

Felid. 

Boltzmann. 

Wullner. 

J. J. Thomson. 

Blondlot. 


Sulphur 


2.56 


Trouton and Lilly. 



•pociflo iMductiire C»paci^ of Iiiqnida. 



Substance. 

Akohola: 

Amyi 

Ethyl 

Methyl 

Ptopyl 

Anifin 

Beojene 

ficDMne averaM about . . . 

Benaene at 5** C 

Bcaune at 15** C. 

Beoaene at 25** C 

Baueoe at 40<* G 

Hexane, between 11"^ and 13<* C. 
Ortane, between 13* .5-14* C. 
Decane, between 13* .5-14* .2 C. 
imylene, between 15* -16* .2 C. 
Octytene, between 11* .5-13* 

.6C. 
Dieeylene, between 16* .7 C. 
(Xk: 

Aiaehid 

Ckstor 

Golia 

lAHDOn. 

Neatafoot 

vJDTe .. .••••*.. 

FetixMecmi ....•••• 

Petroleum ether 

Rape-eeed 

Seaame 

Sperm .. ........ 

TarpcDtine 

Vaadine 

Oiokcrite • .r . . 

Toluene 

Xjieue 



Sp. Ind. Cap. 



15-15.9 
24-27 
32.65 
22.8 
7.5 
1.93-2.45 
2.3 
2.1898 
2.1534 
2.1279 
2.1103 
1.859 
1.934 
1.966 
2.201 
2.175 

2.236 

3.17 
4.6-4.8 

3.07-3.14 
2.25 
3.07 

3.08-3.16 

2.02-2.19 
1.92 
2.2-3.0 
3.17 
8.02-3.09 
2.15-2.28 
2.17 
2.13 
2.2-2.4 
2.3-2.6 



Authority. 



Cohn and Arons; Tereachin. 

Various. 

Tereachin. 

Tereachin. 

Tereachin. 

Various. 

Negreano. 
Neereano. 
Negreano. 
Negreano. 

Landholt and Jahn. 
Landholt and Jahn. 
Landholt and Jahn. 
Landholt and Jahn. 
Landholt and Jahn. 

Landholt and Jahn. 

Hoi>kinBon. 
Various. 
Hopkinson. 
Tomaszewski. 
Hopkinson. 

Arons and Rubens; Hopkin- 
son. 
Various. 
Hopkinson. 
Various. 
Hopkinson. 
Hopkinson; Roaa. 
Various. 
Fuchs. 
Hopkinson 
Various. 
Various. 



38 BVUBOLS, UNITS, INSTKUHBNTS. 

■peclflc iBOBCtl** C«pt>cltj-, — I>efinilion: The ipecific iodueUyi 



spsdty of Ihe suhaUncF with vhith ii 
1). of one voU. The rorfEoicE nr* tables 
en fmiti "»mi1hsoni>n TaLles'' 
of pnper cubits viiri« from 3 to 4. ko 
niitture silopieil. The induFiive caueiiy 
3 lo 3. oQcordmit lo its origin; and mii- 
rile. and olher materials have a capkdl}. 
itnole. lubricBting oil 55 pane, roiia 6«C, 
mdard inductive ca parity of 3.6^ oxidiud 
- _ pitch 70, have 4.4; ArkangH pitch it nelf 
.^e 5.9: a mixture with GBllipot. instead of rosin — for exampte, Callipol 
eOO. Arkaogel pilch 1 10, and Unseed oil 130 — hsi 4,8; n miiiure of lubri- 
cating oil 9. rosin 52, blark owke.ite 23. white oiokerite Itl, has only 3.55. 
The unit of canictW I9 the inleinalional larad. ohii-h ii defined u Ihe 
capBcity of a condeneer wliirb requira one coulomb (1 ampere for 1 second) 
lo raiso its potential from lero lo one volt. 



Fioa. 29 and 30. Standard Condensors. 
As the fvad in far larger than ever is met in pracllce. Ihe ] 



min'o-farads or frattioiii. of (he same. Fig. 


ao [■)iows the ordinary ) micro- 


farad coniicDaer. anil Kik. 30 one that ii t 


..Ijustable (or different valuer. 


Diagram 31 showi an outline of Ihe Conner 


lions inside an adjustable con- 




T is most usually made up of 
ler by some insulator such aa 


sheets of tin toil neparalel from each oth 


paraffined paper or mica. Every altemalp 


sheet of foil is connected lo a 


aimmon terminal. As the eatwcily of a on 
ness of Ihe conductors to each oilier, and u 




pon Ihe aru of llie same, the 
^ and still be safe from kakase 


insulating material is mode Di thin aa ptmibli 


or puncture. Many oheets of (oil are joinni 


tocelher ss d«cril.ed lo m^iEe 








la™a"« M'p^iat^ inio bliidi<S. 



CONDBHSKKS. 



i 



Fio. 32. HodUled Mftscart ElecCrometeT. 



r 



4U BTMBOI^, UNITS, INSTRUMENTS. 

mnd krrucsd k> that bdv of them «an be iduned in or ont to add to or 
IsMan the total capaaty. If connected in tnulliple «■ shown, or if Iba 
poeitive Bde of one condeiaer be eoDoecled to the nwative aide of utotber, 
or a number of them are thiu added together, then the condetLsn are aan 
to be Brraaaed in "cuoade" or in aerin. Thii ia seldom done unl^ it b* 
to nbtiun ir«tor variation in capacity. 

Elect r«aH«ter. — Another uutruraeut uied whsr* i,„ u„vu> 
eleetnacatie capaaliea or potaatiala is eonunon, is the rtectmnitltT. 



"ho wSTi" 



L. The 



mi each other. Oiifntito 
guadnuita are connected by 
nne wirea. A eharee of riec- 

oonneotinc tba ■uspcosioD 
GlamaDt with a Leyden jar 

If the needle be oharKed 
poaitivelv it will be attracted 
by a ne^tive charge and r^ 
pel led by a pontive charweu 
If, therefore, thire ba a At. 



lero. The usual mirror, 

scale. s,nd lamp are uaod 
with this iostrumenl. 

Sown in Fi«.'32. 



>0 T*lt- 
Fio. 33. Kelvin's ElectroeUtie Voltmeter. ^ modificaOon of the els 

ins high, and in aome «hb tow, altematii 
trostaliD voltmeter of Lord Kelvin. It 

In the high potential inslrument. Fig. 33. the needle is made of a thin 
aluminium plale suspended vertically on delicate knife-edgea. with a pointer 
extendiatf from the upper part to a scale. 

On oilher side of the needle, and parallel to its faoe, ate placed two 
quadrant ptila metallically connected snd serving as one terzninal of the 

terminal. Any electrical potenlial dilferencB between the needle and tha 
plates will deflect the needle out of its neutral pantion. Calibraled weights 
can be hung an the bottom ol the needlo to change the value of the acslo 

TOK.I'nfBTBHS. 

These are indicating instruments which ahow the eleetroDKitiv* force 
impraseed upon their lermimils. They are, in nearly all casae, caUbrated 
cafvanomptera of constant high reaiatance. When eonneetsd across the 
terminals of any aouree of electromotive force, currents will flow through 
them which are directly proportional to the Impressed voltocca. A pointer 
connected to the movrng element moves over a st»Io which is empiricelly 
graduated to ahow the impressed voltage. The reaistanoe of eommeroid 



^ 



CONDENSERS. 41 



ToUmetcn in ohms varies from 10 to 160 times the lull scale reading in 
voHs; thus, a voltmeter of Weston's make having a range of 150 volts may 
have a resistanoe of from 15000 to 325.000 ohms. The reaistanoe should be 
vouiid non-induetively and of a wire possessing a negligible temperature 
qpfcffideat. The coBtrolling or directive forces to Ining the pointer back to 
sero are gensrally obtained from springs or gravity and occasionally from 
murneta. 

Inece are several types of voltmeters in commercial use, those devel- 
oped by Edward Weston being j;>erhap8 the best known. For direot- 
cuneat measurements in either switchboard or portable forms the moving 
coil type constructed on the general principle of the d'Arsonval galvanom- 
eter with pivoted coil is most frequently used. They can be constructed 
nss to have high remstanoes and perfect dam|>ing and are but little affected 
by eztstnal fields, especially if shielded with iron casing, as is often done 
whb switchboard instruments. . 

For altemating-ourrent measurements the electromagnetic or soft iron 
iBftniment is very commonly used for switchboard work. ^ In this instru- 
moit a mass of soft iron is so placed in a solenoid that it will be drawn 
irom the center to the edge of the solenoid, or drawn into the solenoid from 
•a outside point. These instruments are correct only for the particular 
freqaeney for which they were calibrated and corrections should be made 
for sny change of frequency. When properly calibrated they may be used 
OB direct-current circuits. 

Pbrtable voltmeters for alternating-current measumnents frequently 
enq>by a sjrstem based upon the electro-dynamometer. This instrument 
lai the advantage of being independent of frequency variations or wave 
fona. It can also be used' for cUrect-current measurements if correction 
(or external fields is made. 

la addition to the above types, voltmeters are constructed on the hot 
wire principle in which the passage of the current causes heating and a 
muequait expansion of the wire tnrouffh which it passes. The expansion 
of the wire is taikexk up by a spring which causes a pointer to move across a 
mduated scalei 



The ecale of a voltmeter may be graduated and marked so as to indicate 
the value of the currents passing through it instead of the volts impressed 
ignn iu terminals. It will then be an ammeter. To be of value its 
nsntanee must be small. Many ammeters consist of moving-cpil milli- 
voltmeters oonnected to the terminals of shunts through which the 
comnta to be measured are passed. The shunts are made of a high resist- 
•ace kiw temperature coefficient alloy and. since the resistance remains 
eoostant. the drop in potential between its terminals will be proportionate 
to the current flowing through it. The scales are graduated so as to indi- 
tate the currents passing through the shunts. The shunt type of instru- 
neat is particularly applicable to switchboards, but is adapted for direct- 
cvrent measurements only. 

For altemating-curreat measurements the electromagnetic systeni is 
RMally employad. the total current to be measured passing through a 
bv<resistanoe solenoid, or the current flowing through the ammeter may be 
redwed by inserting the primary of a series transformer in the mam circuit 
•ad eonneeting the ammeter across the terminals of the secondary. Since 
theatio of current in the primary to that in the secondary is constant, the 
iaimeter may be calibrated in terms of the primary, but need have only the 
mall secondary current flowing through it. «^ :« „ r«o« 

••ft IroM lMatmai«Bt». — If a piece of soft iron be pUced in a mag- 
»e«ie fieM it becomes itself magnetic. This fact is utilized in the so-called 
"soft iron" instruments in wKch the movable system consists of a. soft 
iron needle pivoted within a coil and normally placed oblique to the direc- 
tioaa of its magnetic field. When a current passes through **»« coil the 
awdle tends to assume a position parallel to the lines of force, and being 
«»t«>lled by a spring or other controlling force, the deflection is a measure 

ThL^^SS^oflmrSSmcnt is used to some extent for switchboard work, 
but eamrot be used in measurements where great accuracy is reqmred on 
MBomt of magnetic lag in the iron. 



> 



SYMBOLS, UNITS, INBTRUHENTS. 



- throuffb two ooilB of ivirB, which ars caeai 
h othsr. they will lend to place themidw 

40TI. The Biemen'i eJ«ctro-dynunar 

mmoatiued. It connaU of a fixed o 

nf a few lurns of heavy wire (or heav 

aDd another ot many tun 



ibleof 



Sfi' 



i Ihereto, ig >i; 
nil of few Cur 



lial the degreefl 

The["iower ende of the 

lion with the Bsed 
Bows throiwh the 

IS pontioD at risht 



of angle through 



t dependinc 

■prina, / iB^hl."" *" 
the angle of defiecli 



of the 

Tent, and d be 



The eleetro-d; 

'tematin, ^„,„_ 
. alao di 






Item* tint eurrenia o( 

myable roll ol the eleclro-djmamometBr be of 

led roil be ol heavy wire, then the imtruiiient 
the work of a circuit in watts, by oanaecting 
the circuit under test, and Ihn movable ooil 
■cult. In thia case, if the voltage current be i, 
fiied coil he vi. then the power «1«*1»K^ 

er. H the inovable coil be not brought back 
ted with it be pBrmitTed to move over a grmd- 
calibrated dir^tly in watti. 
tmeter >> oonaCnicCed eubetsntiilly on this 

r (elect ro-dynamometer) mny be reliable for 
DOwer, il ia needful thnt <he fine-wire circuit. 

QCreAsed by adding auxiliary non-induotiva 



CONDEHBERg. 



■ Conysalte Eledrlc Balnnc*. 

rmploycd to B conniileratile exlent u n etftDdard (c 



fafX^wu™' ^tlt h«L9 been almoal enlLrelv guperne-led by Ihe 



acliun KDil tepui- 



■a Stacdnrci CoropusLte Uslanw. 



IningihoHB the tjieory on wliifh tlie "]''''""^?:j^',„ '-i,. „„■ imrlii- a 






yriHD foi 



_. . _ _ llie riKl.t. Wli. 



HCh Wirt 



imiUtc<l;«nH, to an taraflP'^''''?*""''' '" n,nife oi"| 

pllhi-bcam. leovinif it fr«. ,, ._ r. . .i..in.iminBi 

To VtoM ViJlnvlerorCtrUt-amptTrMrlrr. — (A/nBerltueinsttumf< 
Ih. circuit or »ur<* of V.M .F throuEi' a non-mJucl.vB «'''' »|"'1 '';f her 
inllw tollowira '''»«'■■"; 't' 3"'^* "/"/htZThe'wt^«.ntoi^ 
_ One o" tlU weinlil- otr,. r UM. •'™. ''. "i»" 'l";^'!"",™* 'n'l'^l.'^hTr; a 



44 



SYMBOLS, UNITS, INSTRUMENTS. 



) 



lated by a oompariaon of the scale-reading with the certificate accompanying 
the instrument. The volts E.M.F. at the terminals are calculated from the 
current flowins and the resistance in circuit, including the non-inductive 
resistance used, by Ohm's law, v = IR. 

To Uaeaa Hekto-amjiere Meter. — Turn the switch H to ** watts," inisert 
the thick wire coils in circuit with the current in such a way that the right- 
hand end of the beam rises. Use the " sledge " alone or the weight ma^ed 

tD.W, 

Terminals E and ^i are then introduced into the circuit, and a measured 
current passed through the suspended coils a and h ; and the constants given 
in the certificate for the balance used in this way are calculated on the as- 
sumption that this current is .26 ampere. Any other current may be used, 
say 7 ampere, then the constant becomes 7 •+■ .25 or 4 7. 

The current Bowing in the suspended coils g and h may be measured by 
the instrument itself, arranged for the measurement of volts. To do this, 
first measure the current produced by the applied E.M.F. through the ooiU 




VWSAAAAA/ ' 

SI *' 

Fig. 36. Diagram of the Kelvin Composite Balance. 



of the instrument and the external resistance, then turn the switch IT to 
** watt," and introduce into the circuit a resistance equal to that of the fixed 
coils. 

To Uae <u a WaUmeter. — Insert the thick wire coils in the main circuit ; 
then join one end of the non-inductive resistance B to one terminal of the 
fine wire coils, and the other end of /2 to one of the leads ; the other termi- 
nal of the fine wire coils is connected to the other lead. The current flowing 
and the E.M.F. may now be determined by the methods described above. 
The watts can then be calculated from the F^M.F. of the leads, and the 
current flowing in the thick wire coils by the formula, 

P^=Vr — i IR, 

Where i = current in the suspended coil circuit. 
7 = current in the thick wire coils. 
R = resistance in the circuit. 

When working with alternating currents the non-inductive resiiitance R 
must be large enouj^h to prevent any difference of phase of the current 
flowing in the fine wire coils and the E.M.F. of the circuit. 



DOUBLBD SQUARE BOOTS. 



46 



SMile 9t ]»*«ble« S^vare 



r«r liimA KelTte*» Stead- 








100 


200 


300 1 


400 


600 


600 


700 


800 


900 






O.00O 


20.00 


28.28 


34.64 


40.00 


44.72 


48.99 


62.92 


66.57 


60.00 







2jOOO 


20.10 


28.36 


34.70 


40.06 


44.77 


49.03 


52.96 


56.60 


60.03 


1 




2.828 


20.20 


28.43 


34.76 


40.10 


44.81 


49.07 


52.99 


66.64 


60.07 


2 




3.464 


20.30 


28.50 


34.81 


40.16 


44.86 


49.11 


63.03 


56.67 


60.10 


3 




4.000 


20.40 


28J}7 


34.87 


40.20 


44.90 


49.15 


53.07 


66.71 


60.13 


4 




4.472 


20.40 


28.64 


34.93 


40.26 


44.94 


49.19 


63.10 


66.75 


60.17 


6 




4.880 


20.60 


28.71 


34.99 


40.30 


44.99 


49.23 


63.14 


56.78 


60.20 


6 




8.292 


20.69 


28.77 


35.04 


40.35 


46.03 


49.27 


53.18 


66.82 


60.23 


7 




5.867 


20.78 


28.84 


35.10 


40.40 


45.08 


49.32 


53.22 


56.86 


60.27 


8 




8.000 


20J» 


28.91 


36.16 


40.45 


45.12 


49.36 


53.25 


66.89 


60.30 


9 


10 


6.325 


WM 


28.98 


35.21 


40JS0 


45.17 


49.40 


53.29 


66.92 


60.33 


10 


u 


6.63S 


21X7 


29.06 


85.27 


40.56 


45.21 


49.44 


68.33 


66.96 


60.37 


11 


12 


6.928 


21.17 


29.12 


36.33 


40.60 


45.25 


49.48 


63.37 


66.99 


60.40 


12 


13 


7J11 


21.26 


29.19 


36.38 


40.64 


45.30 


49.52 


63.40 


67.03 


80.43 


13 


M 


7.483 


21.36 


29.26 


36.44 


40.69 


45.34 


49.66 


63.44 


67.06 


60.46 


14 


15 


7.746 


21.46 


29.33 


35.50 


40.74 


45.38 


49.60 


53.48 


67.10 


90JSO 


16 


IS 


8jOOO 


21.54 


29.39 


36.55 


40.79 


45.43 


49.64 


53.62 


67.13 


eoja 


16 


17 


8.346 


21.63 


29.46 


35.61 


40.84 


46.48 


49.68 


63.56 


67.17 


60.56 


17 


18 


8.486 


21.73 


2dJa 


36.67 


40.89 


45.62 


49.72 


53.59 


67.20 


60.60 


18 


If 


8.718 


21.82 


29.60 


35.72 


40.94 


45.56 


49.76 


53.63 


67.24 


60.63 


19 


% 


8.944 


21.91 


29.68 


36.78 


40.99 


46.61 


49.80 


63.67 


67.27 


60.66 


20 


& 


9.166 


22.00 


29.73 


36.83 


41.04 


45.66 


49.84 


63.70 


57.31 


60.70 


21 


SS 


9.381 


22.09 


29.80 


36.89 


41.09 


45.60 


49.88 


63.74 


67.34 


60.73 


22 


SI 


9JW2 


22.18 


29.87 


35.94 


41.13 


45.74 


49.92 


63.78 


67.38 


60.76 


23 


M 


9.798 


22.27 


£•2 

80.06 


36.00 


41.18 


45.78 


40.96 


63.81 


67.41 


60.79 ' 24 


S 


IOjOOO 


22.36 

• 


36.06 


41.23 


45.83 


50.00 


63.86 


67.46 


60..83 
60.86 


26 


18 


10.198 


22.46 


3Oj07 


36.11 


41.28 


45.87 


50.04 


53.89 


57.48 


28 


27 


10.392 


22M 


30.13 


36.17 


41.33 


45.91 


50.06 


53.93 


57.62 


60.89 


27 


28 


10583 


22.83 


30.20 


36.22 


41.38 


46.06 


60.12 


53.96 


67.65 


60.93 


28 


28 


10.770 


22.72 


30.27 


36.28 


41.42 


46.00 


60.16 


64.00 


57.58 


60.96, 29 


88 


10.964 


22.80 


30.33 


36.33 


41.47 


46.04 


50.20 


64.04 


67.62 


eoM 


30 


« 


11.136 


22.89 


30.40 


36.39 


41.52 


46.09 


50.24 


64.07 


67.66 


61.02 


31 


82 


11.314 


22.98 


30.46 


36.44 


41.57 


46.13 


60.28 


64.11 


57.69 


61.06 


32 


3S 


11.489 


23.07 


30.53 


36.60 


41.62 


46.17 


50.32 


54.15 


57.72 


61.00 


33 


81 


11.602 


23.15 


30.50 


86Ji6 


41.67 


46.22 


5036 


64.18 


67.76 


61.12 


34 


m 


11.832 


23.34 


30.66 


36.61 


41.71 


46.26 


50.40 


54.22 


57.79 


61.16 


36 


38 


120)00 


23.32 


30.72 


36.06 


41.76 


46.30 


50.44 


54.26 


57.83 


61.19 


38 


37 


12.166 


23.41 


30.79 


36.72 


41.81 


46.35 


60.48 


54.30 


57.88 


61.22 


37 


88 


12.329 


23.49 


30.85 


36.77 


41.86 


46.38 


50.52 


54.33 


57.90 


61.25 


38 


98 


12L480 


23.58 


30.92 


36.82 


41.90 


46.43 


60.56 


64.37 


57.93 


61.29 


39 


48 


12.849 


23.66 


30.98 


36.88 


41.06 


46.48 


60.60 


64.41 


57.97 


61.38 


40 


41 


12.808 


23.75 


31.06 


36.93 


42.00 


46.62 


60.64 


54.44 


58.00 


61.35 


41 


42 


12.961 


23.83 


31.11 


36.99 


42.06 


46.56 


fiO.68 


54.48 


58.03 


61.38 


42 


a 


13.115 


23.92 


31.18 


37.04 


42.10 


46.60 


60.71 


54.62 


58.07 


61.42 


43 


44 


13.268 


24.00 


31.34 


37.00 


42.14 


46.65 


60.76 


64.55 


58.10 


61.45 


44 


4B 


13.416 


24j08 


31.30 


37.15 


42.19 


46.69 


60.79 


54.69 


58.14 


61.48 


46 


48 


13^665 


24.17 


31.37 


37.20 


42.24 


46.73 


60.83 


64.63 


58.17 


61.51 


46 


47 


13.711 


24.25 


31.43 


37.26 


42.28 


46.78 


60.87 


54.66 


68.21 


61.55 


47 


48 


13.868 


24.33 


31.50 


37.31 


42.33 


46.82 


50.91 


64.70 


68.24 


61.68 


48 


48 


14M00 


24.41 


31.56 


37.36 


42.38 


46.86 


60.95 


64.74 


58.28 


61.61 


49 


68 


14.148 


24.49 


81.62 


37.42 


42.43 


46.90 


50.99 r>4.77 


58.31 


61.64 


60 



46 



8TMB0L8, UNITS, INSTBUMEKTS. 








100 


200 


300 


400 


500 


600 


700 


800 


900 




51 


14,283 


24.58 


31.69 


37.47 


42.47 


46.95 


51.03 


64.81 


68.34 


61.68 


61 


52 


14.422 


24.66 


31.75 


37.52 


42.52 


46.99 


51.07 


64.85 


68.38 


61.71 


62 


53 


14.560 


24.U 


31.81 


37.58 


42.57 


47.03 


51.11 


64.88 


68.41 


61.74 


63 


54 


14.697 


1M.82 


31.87 


37.63 


42.61 


47.07 


51.16 


64.92 


68.45 


61.77 


64 


55 


14.832 


24.90 


31.94 


37.68 


42.66 


47.12 


51.19 


64.95 


68.48 


61.81 


66 


56 


1 14.967 


24.98 


32.00 


37.74 


42.71 


47.16 


51.22 


54.99 


68.51 


61.84 


56 


57 


15.100 


25.06 


32.06 


37.79 


42.76 


47.20 


51.26 


55.03 


68.55 


61.87 


67 


58 


15.232 


25.14 


32.12 


37.84 


42.80 


47.24 


51.30 


55.06 


58.58 


61.90 


58 


59 


15.362 


25.22 


32.19 


37.89 


42.85 


47.29 


51.34 


65.10 


68.62 


61.94 


69 


60 


15.492 


25.30 


32.25 


37.95 


42.90 


47.33 


61.38 


65.14 


68.65 


61.97 


60 


61 


15.620 


25.38 


32.31 


38.00 


42.94 


47.37 


51.42 


65.17 


68.69 


62.00 


61 


62 


15.748 


25.46 


32.37 


38.05 


42.99 


47.41 


51.46 


65.21 


68.72 


62.03 


62 


63 


15.875 


25.58 


32.43 


38.11 


43.03 


47.46 


51.50 


56.!U 


58.75 


62.06 


63 


64 


16.000 


25.61 


32.50 


38.16 


43.08 


47.50 


51.54 


66.28 


58.79 


62.10 


64 


65 


16.125 


25.69 


32.56 


38.21 


43.13 


47.54 


51.58 


66.32 


68.82 


62.13 


66 


66 


16.248 


25.77 


32.62 


38.26 


43.17 


47.68 


51.61 


65.35 


68.86 


62.16 


66 


67 


16.371 


25.85 


32.68 


38.31 


43.22 


47.62 


61.65 


65.38 


68.89 


62.19 


e7 


68 


16.492 


25^ 


32.74 


38.37 


43.27 


47.G7 


51.69 


65.43 


68.92 


62.23 


68 


69 


16.613 


26.00 


32.80 


38.42 


43.31 


47.71 


51.73 


65.46 


68.96 


62.26 


69 


70 


16.733 


26.08 


32.86 


38.47 


43.36 


47.75 


61.77 


66.60 


68.99 


62.29 


70 


71 


16^2 


26.15 


32.92 


38.52 


43.41 


47.79 


61.81 


65 J» 


69.03 


62.32 


71 


72 


16.971 


26.23 


32.98 


38.57 


43.45 


47.83 


61.85 


65.67 


69.06 


62.35 


72 


73 


17.088 


26.31 


33.05 


38.63 


43.60 


47.87 


51.88 


56.61 


69,09 


62.39 


73 


74 


17.205 


26.38 


33.11 


38.68 


43.54 


47.92 


61.92 


65.64 


60.13 


62.42 


74 


75 


17.321 


26.46 


33.17 


38.73 


43.59 


47.96 


51.96 


66.68 


69.16 


62.46 


76 


76 


17.4;J6 


26.53 


33.23 


38.78 


43.63 


48.00 


62.00 


65.71 


69.19 


62.48 


76 


77 


17.550 


26.61 


33.29 


38.83 


43.68 


48M 


62.04 


66.76 


59.23 


62.61 


77 


78- 


17.664 


26.68 


33.35 


38.88 


43.73 


48.08 


52.08 


65.79- 


69.26 


62.55 


78 


79 


17.776 


26.76 


33.41 


38.94 


43.77 


48.12 


52.12 


65.82 


59.30 


62.58 79 


80 


17.889 


26.83 


33.47 


38.99 


43.82 


48.17 


62.15 


65.86 


59.% 


62.61 


80 


81 


18.000 


26.91 


33.63 


39.04 


43.86 


48.21 


62.19 


65.89 


69.36 


62.64 


81 


82 


18.111 


26.98 


33.59 


39.09 


43.91 


48.25 


62.23 


66.93 


69.40 


62.67 


82 


83 


18.221 


27.06 


33.65 


39.14 


43.95 


48.29 


52.27 


66.96 


59.43 


62.71 


8» 


M 


18.330 


27.13 


33.70 


39.19 


44.00 


48.3:1 


52.31 


66.00 


69.46 


62.74 


84 


85 


18.439 


27.20 


33.76 


39.24 


44.05 


48.37 


52.36 


66.(H 


59.50 


62.77 


85 


86 


18.547 


27.28 


33.82 


39.29 


44.09 


48.41 


62..38 


66 07 


59.53 


62.80 


86 


87 


1S.&55 


27.35 


33.88 


3Q.M 


44.14 


48.46 


62.42 


66.11 


69.57 


62.83 


87 


88 


18.702 


27.42 


33.94 


39.40 


44.18 


48.50 


62.46 


66.14 


59.60 


62.86 


88 


80 


18.868 


27.50 


34.00 


39.45 


44.23 


48.54 


52.50 


56.18 


59.63 


62.90 


89 


90 


18.974 


27.57 


34.06 


39.50 


44.27 


48.58 


52.54 


66.21 


69.67 


62.93 


90 


91 


19.079 


27.64 


34.12 


39.55 


44.32 


48.62 


62.57 


56.26 


69.70 


62.96 


91 


92 


19.183 


27.71 


34.18 


39.60 


44.36 


48.66 


62.61 


66.28 


69.73 


62.99 


92 


93 


19.287 


27.78 


34.2,J 


39.65 


44.41 


48.70 


52.65 


66.32 


59.77 


63.02 


93 


94 


19.391 


27.86 


34.29 


30.70 


44.43 


48.74 


52.G9 


66.36 


59.80 


63.06 


94 


95 


19.494 


27.93 34.;« 


30.75 


44.50 


48.79 


52.73 


50.39 


59.83 


63.09 


95 


96 


19.500 


28.00 


34.41 


39.80 


44.54 


48.83 


52.76 


56.43 


69.87 


63.12 


96 


97 


19.698 


28.07 


34.47 


30.85 


44.59 


4S.87 


52.80 


56.46 


59.90 


63.15 


97 


98 


19.799 


28.14 


34.53 


39.1K) 


44.rt3 


48.91 


52.84 


56.50 


59.93 


63.18 


98 


99 


19.900 


28.21 


34.58 


39.95 


44.68 


48.95 


52.88 


56.53 


59.97 


63.21 


99 


100 


20.000 


28.28 


34.64 


40.00 


44.72 


48.99 


62.92 50.67 


60.00 


63.25 


100 



THE POTENTIOMETER. 47 

In its simplest form the potentiometer may be represented by the dia- 
gnm. Fig. 37. 

A B la & resistance in which a constant current from the battery IF is 
znalntained. The regulating resistance R is used to compensate for varia- 
tions in the E.M.F. or internal resistance of the battery W. The con- 
stancy of the current in yl B is checked by seeing that the drop in poten- 
tial between two points chosen in it is equal to tne E.M.F. of a standard 
oelL The standard cell is introduced into the circuit M. E. M.' tit E^ and 
the regulating resistance R adjusted until the sensitive galvanometer O 
shows no deflection. Assuming A B to have a uniform resistance through- 
out its length, and the current in it to remain constant, it is obvious that 
any other voltage not greater than the drop between A and B can be 
measured by introducing it at E and shifting the points MM' until the 
gahrmnometer again comes to a balance. Further, a direct reading scale 
may be placed between A and B, For 

most potentiometer work the drop i iL 

between A and B is made about 1.5 | A 



volts, as this is about the E.M.F. of a/a/vw^aaaa/v ^ 

a standard Clark cell. That the instru- | m " VT 

ment may have a wide range and ■" ^ 



B 



ment may have a wide range and '^ + 

make measurements to a sufficiently p /^^^ 

high degree of accuracy, it is neces- 1— o o ( t V- — ' 

sary that it be possible to sub-divide V_>^ 

this resistance, so as to read voltage -r. 07 

to at least the fifth decimal place. '*"• ^'• 

Since the current must be kept constant the total resistance in the circuit 

must not be varied by raising the resistance between M and M\ 

SaaC** — To meet general laboratory requirements the potentiometer 
must measure directly as high as 1.5 volts so that all kinds of standard 
cells may be compared with each other; and it must measure as low as 
.00001 volt so that reasonably )ow_ resistance standards may be used in 
measuring current. An example will make this point clear. To measure 
1000 amperes the current must flow through a standard low resistance 
and the drop in E.M.F. across its terminals be measured on the potentiom- 
eter. With a potentiometer reading only to .0001 volt the drop across 
the low resistance must be at least .1 volt in order that it may be read to 
an accuracy of ^%. If 1000 amperes is the maximum current to be used 
on the particular low resistance it should be so designed as to give proper 
readings with a minimum current at least as low as 100 amperes. 100 
amperes must consequently give a drop of .1 volt, which fixes the resistanceat 
Ml ohm. .001 ohm to carr^ 1000 amperes must be able to dissipate 1000 
watts, and in order to remam a standard it must do this without heating 
enough to vary the resistance outside of small limits. With a potentiometer 
reading to .00001 volt the same range of current can be handled on a resist- 
ance of .0001 ohm and can be measured to the same degree of accuracy. 
To carry 1000 amperes it will only have to dissii>ate 100 watts. To maintam 
the same degree of accuracy while a current is flowing it can consequently 
be made of a very much smaller size and with -t^^he radiating surface. 

Methods of VJslnir tli« Standard Cell. — The standard cell is 
used to measure the current flowing through the potentiometer, which is 
done by making the drop in E.M.F. across a known resistance in the circuit 
equal to that of the standard cell. 

Ist Method. — The standard cell maybe used as indicated in Fig. 38. 
The gialvanometer is permanentiv in circuit with the points 3/ A/', and by 
meanii of the double-throw switch U the standard cell *S', or an unknown 
E.M.F. Et may be thrown into the same circuit. If the resistance A B is 

Sovided with a scale by means of which it is sub-divided into, for example, 
,000 equal parts, the points MM* may be set to a reading corresponding 
to the E.M.F. of the standard cell and the current from the battery 
W reipilated by the resistance R until there is a balance, the standard cell 
beins in circuit with the galvanometer and points MM'. There will then 
be such a current flowing that for any other position of the points MM', 
producing a balance with the unknown E.M.F. in circuit, the reading from 
the scale will be direct in volts. This method is open to the objection that 
it requires a resetting of the points MM' to make a check measurement 
of the current flowing. In making accurate measurements these check 



48 



SYMBOLS, UNITS, INSTRUMENTS. 



moamirementfl have to be made frequently and are especially inconvenieat 
by this method when the points Mm* are multiplied from two to four or 
five as they generally are. 

2d Method. — A meihod of measuring and checking the currents whidi 
avoids this objection is shown in Fig. 39. It is not necessary that the re- 
sistance which furnishes the drop, against which the E.M.F. of the standard 



i^ M^iB ijHAlv « 





Fxo. 38. 



Fio. 39. 



eell is balanced, be between the points A B, which limit the motion of MM'. 
If placed at lU and proi>erly cnosen with reference to the E.M.F. of the 
standard cell and the resistance of the wire A B, the current which pro- 
duces a drop across it equal to the E.M.F. of the standard cell will make 
the scale of A B direct reading in volts. In this case the double-throw 
switch is arranged so as to thvow the galvanometer eithor into the circuit 
containing the standard cell and the resistance R*, or into the circuit con- 
taining the points MM' and the imknown E.M.F. This method is, how- 
ever, open to a serious objection from the standpoint of accuracy, which 
is avoided by the first. To illustrate this by a numerical example, assume 
in both cases all the resistances adjusted to an accuracy of ^ of 1% and 
the error to be in such a direction as to produce the worst result. In the 
second method if the resistance R* were ^% high the current flowing 
through the potentiometer would be A% lower than it should be. If now 

the resistances of A B were i^% low this 
would introduce a second error of the 
same amount in the same direction 
and the resulting error in measurement 
would be A%> Iq other words the 
measurement accuracy throughout the 
range of the potentiometer may be 
only half so good as the adjustment 
accuracy. In the first method, since 
the standard cell E.M.F. and the un- 
known E.M.F. are balanced against 
the drop across the same resistances 
in meastuing an E.M.F. nearly equal 
to that of the standard cell, inaccura- 
cies in the resistance are the same in 
both cases and balance each other, 
measurements are bound to be more 

In a potentiometer 




Fio. 40. 



Consequently by this method measurements are 

accurate than the adjustment of the resistances. 

arranged to be used with a Clark cell using the first method of applying 
the standard cell and with resistances adjusted to A% it can be shown by- 
calculation that the maximum error in measurement will vary with the 
value of the E.M.F. under measurement. For E.M.F. of 1.5 volts this 
crrorwill be less than .003%. For E.M.F. of 1.2 volts it will be about .01%. 
For E.M.F. of .8 volts it will be about .02%. For E.M.F. of .3 to .1 volts 
It will be .04%, and in no case will be larger than this. To sum up the con- 
trast in accuracy between the two methods: in the second the errors may 
be twice as great as the adjustment errors throughout the range, while in 
the first method they only become this larae for .3 volt and under, and for 
higher voltages have increasing accuracy becoming equal to that of the 
adjustment at .8 volts and much better as they approach the E.M.F. of 
the standard cell; at exactly the E.M.F. of the standard cell the accuracy 
of comparison becomes independent of the accuracy of adjustment of the 
resistance. 



DST1ESMINATION OF WAVE FORM. 



49 



ad Method. -—A third method combines with the aoouracy of the firet. the 

JS!lS!!KSi'*'. l^ *25**- ?*"'»»f"»t«tedinFig.40. Tli E.M.F. b? tS 
stABdani edl u balanMd against the drop across a part of the potentiometer 



wire ii/^ asm method No. 1, but the termmals of this resistance are found, not 
^* k R*??^ ^ W' ****.* *^*y *" permanently fixed, and the double- 



♦wlf— ^!^*;iX" /VTiT TL* "V "**'*'' "^"" Kj»*u»««?uwjr IM.I3U. fuia cne aouoie- 

tArra- switch U throws the galvanometer mto one circuit or the other as de- 



AA TtMllNALS 



OJT WAITS FORM or cimiftMirv 

KliBCXliOMOTKVJB f OJROM. 

TBSBS are numerouB methods of determining ware form, those used in 
uboratm experiments commonly making use of the ballistic galranometer. 
Of the siinple methods used in shop practice, R. D. Mershonrof the West- 

*W?^?®***'^^*?*l^*°^*®**^"K ^'* *>»■ applied the telephone to an 
Old DalUatIc method in such a manner as to make it quite accurate and 
readily u^plied. 

McnteB'a Method.— The following cut shows the conneoUons. A 
telephone receirer, shunted with a condenser, is connected in the line from 
the Bonrce of current, the wave form of which it is wished to determine. A 
eoatact-^iaker is placed in the other leg, and an external source of steady 
earrent, as from a storage battery, is opposed to the alternating current, tm 
shovB. The pre^ure of the external current is then varied until there is 
BO sound in the telephone, when the 
pcesnres are equal and can be read 
from the voltmeter. The contact- 
maker being revolved by successive 
itMs, pointB may be determined for an 
oittre cycle. ^^ 

•■McauB'a H«tb9d. — Where it 
ii desirable to make simultaneous de- 
teradnatioiis it will ordinarily require 
several contact-makers, as well as full 
sets of instruments. Dr. Louis Dun- 
can baa devised a method by which one 
eoolact-maker In connection with a 
dvnamometer for each curve will ena- 
Ne all readings to be taken at once. 
The following cut shows the connec- 
tkine. The nxed coils of all the dy- 
aamcnneterB are connected to their 
reqieetive circuits, and the fine wire 
iMvablecoila of atwut 1,000 ohms each, 
are connected in series with a contact 
■laker and small storage battery. The contact-maker is made to revolve in 
■yacbronism with the tutemating current source. Now, If alternating cur- 
nuts frcwk tbe different sources are passed through the fixed coils, and at 

intervals of the same frequency current from 
the battery is passed through the movable coils, 
the deflection or impulse will be in proportion 
to the instantaneous value of the currents 
flowing in the fixed coils, and the deflections of 
the movable coils will take permanent position 
indicating that value, if the contact-maker and 
sources <n alternating current are revolved in 
unison. 

The dynamometers are calibrated first by 
passine continuous currents of known value 
through the fixed coils, while the regular in- 
terrupted current from the battery is behig 
passed through the movable coils. 

JRym'a Jtetliod.— Prof. Harris J. Ryan, 
of Cornell university, designed a special elec- 
trometer for use in connection with a very fine 
series of transformer tests. This instrument 
. ^ ^ . . ^^1 ^ found described and illustrated in the 

chapter on desoriptioii of instruments. 




Fio. 41. Mershdn's method of d^ 
termining Wave Form. 




Fio. 42. Duncan's method 
of determining curves 
of several circuits at the 
time. 



60 



STUB0I.8, UXIT8, IXSTRUHEITTS. 



• ■w«n«rtmMftn 



The method of using it is shown in the cut below, in which the contact- 
maker shown is made to revolve in a^'nchroniam with the source of alter* 
nating current. The terminals, d di, of the indicating instruments can be 
connected to any one of the three sets of terminals, o Oi, 6 &i, e C|. 

The terminals, a ai, are for readinjg 
the instantaneous value of the pri- 
mary impressed E.M.F.; b 6|, the 
same value of the current flowing 
through the small non-inductive re- 
sistance, R\ and c Ci the same value 
of the secondary impressed E.M.F.; 
the secondary current being read 
from the ammeter shown. Of course 
if the contact -maker be cut ou t, then 

all the above values will be 's/meau^* 




nTTTTTTT 



A.C.AMICTtK 



Rosa Carre Tracer. 



IVAN ILECTMHCTU 



Fio. 43. Prof. Ryan's Method of 
obtaining Curves of Wave Form 
for studying Transformers. 



This instrument consists of a hard- 
rubber cylinder upon which is wound 
a single layer of bare wire. A con- 
stant current from a small storage 

battery is sent through this coil causing a uniform drop of potential be- 
tween its ends. (See Diagram, Fig. 44.) A voltmeter connected between 
the terminals indicates the drop, and the resirttance R in series with the 
battery serves to regulate this drop. The current to be plotted passes 
through the non-inductive resistance A B and the problem is to meajnure 
the instantaneous values of the drop between these two points at succes- 
sive instants throughout the perioii of a wave. The point B is joined to 

the middle point Q of the spiral wire ^fN, 
A is joined through the revolving contact'^ 
maker C M to a sliding contact P. 

The contact-maker is joined to the 
shaft of the alternator, or is at least 
driven in synchronism with it; then 
every time tne contact is completed at 
any pmrticular phase of the wave, the 
current has the same value and the gal- 
vanometer will show a deflection. If 
the sliding contact P be adjusted so that 
the galvanometer shows no deflection, 
then the potential diff'erence between the 
points P and Q is the same as that 
between the points A ami B. Tliis value 
is proportional to the distance P Q, and 
is positive on one side and n^ativo on the other side of Q. 

For making the record, a cylinder is arrangc<l opposite the potentiom- 
eter wire and slider, upon which the paper for the record is wound. A 
tripping point is attached to the slider in such manner that when the gal- 
vanometer has been brought to zero by the adjustment of the resistance /?. 
the pointer is tripped and a point impre^scxl on the record paper through 
a typewriter ril)lD<m, and at the same time the record cvlinder is advanced 
a notch or series of them as may he renuirwi, ready for the next record. 
By this means the plotting of a curve of current or potential takes but a 
few seoomls. 

OMcillocrapli- — Tljis form of instrument devised byBlondel and others 
is much used for the analysis of wave forms of current and electromotive 
force, and for the study of potentials anfl other properties of alternators 
or other forma of dynamos and motors. It is extremtly sensitive and will 
detect and show either on a screen or a photograph, the most minute varia- 
tions in current and potential. Tlie Blondrl t>'pc described below will 
serve to show all the principles of the instrument- Durlell has somewhat 
improverl upon this one. anrl the Grnrral Electric Co, has designed another 
that is especially adapted to workshop practice. 




Fio. 44. Rosa Curve Traoer. 



DBTEKHIKATION OF WAVE FORM. 



ThengrsTini; (Fif. 46)shoi>a tbe Mtieral Kppeaninn of the OKtllognph. 
Thaappuatiu IS mounted in a box (Pig. 4a)wjth an ani lamp at ona tnd. 
Abore a a crouDd-slaBa screen upon which the wftve Fonns are ti^ced by 




Tia. 46. Blondel Osoillograph, 



■ ipol of light. The magrnal ^ 

the poles are placed two aimil 
inm bridaa-piece which rende 



mounlsd on the left in an iaveited jsoaitioD 
made up o( six horaeahoe pieces. Betweei 
,r aetH of vibratioR bands, separated by ai 
s ewh one im iudependent uikil. in thi 



> 



BTUBOLSj UHITB, 



UrSTBUHENTS. 



ud eumot. knd ■» leen on ta 

Ths HTftngeDHat of moUDliiii 

fine and nturow itiip of soft in 

nnd one five-bundrcdlh of an 



LM, Bucb HI (Jib eleotR>nu>tiT« fOTM 

in Iheir rdativa ru— irir^n- 
seeoin.Fig.47; t 



LS band ia a "nry 

i ibiek. fiiis l»nd ie heJd in a mov- 
abla BUppon in a verticsJ position be- 
tween the polen of Lh« taAgnet, It 



ftt a to a Blidlng piece which ma 
■ reotansular groove. The slidi 
rice a rod n above, which pa aa ec 






■o that by turmo 
ia atrelohed more 
bridcCB. The b» 



ntainsl in a tubL 



of Ivory, which Gta into | 
the nudnet poln and a 
about Sy the collar D. 



D the 
a a small 
~he mirror 

oil boi T 

be turned 

nucn ett-ve to coneentraie the field; 
tt £ ia a lene placed in front of tbe 
□itror. In tins way the aoft iron 
Hece vibratee without the use of piv- 
>tg or suBpension. Each horiiontal 

na^net, and the deflections produced 
}y the Doib socumulale from the ex- 
^remitiea to the ceutv of the baud. 

ddenbly. The toUl deflecliona in- 
iicated by the mirixir are propor- 
JODsl to tbe current. Owing (o the 
)ropertiefl peculiar to vibrating bands 

Blondel O^lo^aph, ^hL"^ "fifnhwTZLSi ty^'ib? ES^- 

poution in the inacnetio fidd. Where 

it be affected by 



, and the higher t' 
n Fig. 4S. 



"tw^'dHarei 



ncillographs which a 



j«. Atlw ia an tuiJuBtsble i 
form the beae line of the c 
g the vibrating banr). a per 



tlone. which will answer in moat ou 
irrwilar. The wmsitivEncm in the 
of the spot of light of 100 millimeM 



e the pole-piecea. built of 
the atrip. Th«e are two 
lotion in (he center, tbiu 
quite independent of aach 
ray. The oil tube T oon- 

. On the left is geea™e 
:ical opening Co allow ' 



15.000 T^"" 
cave fot 



— sacoDd 
o the band. 

20.000 viim. 



ia geoflrally brought U 
Ibkl the band haa ai 



DBTKRMI.VATIOM OF WAVE FORM. 

Ok band it nol yM iBtunud. than d«(ir«u« when ihe muneiiulJ 

. . ■ ._, rapidly tbmn the fidd Mrmglh. Tlie numl 

^ [»pidly at first, then iloirly, u I 



1 
i 



fn. 18. Blondel OMiUasrkph, ahowing the Amncemant ol the Macnet. 



itrip. lltey hava dow bwD nduoed a 

0.5 mUliowtcr bixh, ^th a thiclcoflaB of but u.uo to u.i mijiimQcer. Diirer«a 
•ha or mica ia ussd, aod ths miironi are fastened to Hie bands with BbelJao 
Btfcn the toiler are mourned. Aa the baad i> enclowd in so oil box it 
■ tm from mat and wall protected. The eensilivenna dF the initniment 
j mj be creatly varied by usinB an iron yoke which is placed against the 

iltiie firld at the poln. 

. To U» lisbl of Ihe bol irill b« seen the arrangement of the oscillating 
I wrar rnbiA Dvea Che (o4iHi-fro motion to tha HWt o( light in order to 
I fccni the wmTB. The device will be understc-^ ■-- ■'■--'^ — -- ^■■' ■" 

Stta arc lamp whieh throws a beam of light 
' iiBtter F upon the mirror of the oscillograph i 

'ud tmmtt throuih the lios /. falling on the OKiiiBiitv mirror m | 
I Hbind it. The latter i* given s to-and-fro motion by a small synchi 
~" ' m of light thus far has two movemenW, one by the i 



• oi the oeeillocniph and the other by Ihe 
. ibf two giv«0 the wave form which b ] 



ited above on iba ground-glaai 



1 



54 



SYMBOLS, UNITS, IXSTKUMENTS. 



BcreOD P. The to-and-fro movement of the mirror is obtaiaed by a cam 
fixed to the motor-shaft. During two complete periods of the wave the 



"t 







Fio. 49. Diagram showing the Arrangement of the Apparatus in the 

Blondel Oscillograph. 

mirror must be moved at a continuous rate from top to bottom, and during 

the next period it must be able to return so as to continue the movement 

(as will be noticed on the photograph two 
complete waves are throvoi on the screen). 
This is carried out by the profile of the 
cam which is such that the mirror has a 
uniform movement during two cycles of the 
wave, and the next cycle is occupied by the 
return of the mirror (during this time an 
electrically operated shutter placed at F cuts 
off the light), so that the eye perceives only 
a continuous trace of the wave. To observe 

phenomena which are not periodic the motor is replaced by a pendulum 

device. 




Fid. 60. 



r 



MEASUREMENTS. 

Rbvued bt W. N. Goodwin, Jr., axd Pbof. Sam ukl Shbldoit. 



is the fundameDtal law of electrical ciroiiita and is ezprened t 
ID the following equations. 

R 
E = IR 

«=? 

where / = Current strength in amperes, 

R ^ Resistance in ohms, 
E = Electromotive Force in volts. 
The oonductance of a conductor is the reciprocal of its resistance, and 
tltt unit is called a mAo, so that Ohm's law may be stated as follows: 

I=BO 
where O = conductance in mhoa. 

Maltlpl« Gii«aMa. — The oonductance of any number of circuits in 
psimDd is equal to the sum of the conductances of the individual drouits. 
which is, as stated abore, the reciprocal of their resistanoes. The combined 
raastanee then is the reciprocal of the conductance thus found. 
Thus in Fi^. 1, if r and ri be two resistances in 

pscsllel, the oombLned renstance = ^ 1 = , ^ « 

1 , J. r-\-n 

r n 
The joint reodstanoe of any number of resistanoes 

in parallel as a, b, c, and d is 



1_l1_i_1_i_1_i_ * 
a+6 + c+d + **^ 




C«rreBt Im m MslMple CIrcatt is divided Fio. 1. 

unoQg the separate circuits in direct proportion to 

respective conductances, or inversely as their resistances. 

In Fig. 2, the total resistance of circuit 




£"= 



'v total current 



r-i-n 
j^ J?(r + r,) 



and i =: 



En 



Rr + Rri+ m 



%t = 



Er 



Rr -t- Rri + m 



Fio. 2. 



Rr + Rn + m 

a^v» AiK 

Vfrat litter. — If in any circuit a number of currents meet at a point, 
the sum of those flowing toward that point is equal to the sum of those 
flowing away from it. 

Sc^m4 MtAir. — In any closed circuit, the algebraic 
mm of the products formed by multiplying the re- 



^i»ri^ 



VWiV^AW^AAAX 



SMtanoe of eaeh part by the current passing through 
it is equal to the sum of the electromotive forces m 
the dreait. 

By means of these laws, the current in any part of 
sa intricate system of conductors can be founa if the 
resistanoes of the different parts and the electromotive 
iorees are fliyen. I 

Thus in Fig. 8, according to the first law i = t| + ia — 1 

aad from the second law t={i ^ is and from the secona 

law E^uTi and iitt =iiri. Fio. 8. 

From these three formuls, the three unknown currents can be dedused 
Toe sanae method can be applied to more complex drouits. 

5fi 



56 



MEASUREMENTS. 



RSAUTAirCB MMAMMJMMMMM'Em. 



Metli«d* — This is the nrnplcet method of measorinc 
resietanee. The resistaaoe to be measured is inserted in aeries with a 

Sulvanometer and some constant source of current, and the ^Ivanomeier 
eflection noted; then a known adjustable resistance is substituted for tiie 
9 unknown and adjusted until the same deflection is acain obtained. Then 
this value of the adjustable resistance is equal to that of the resistanoe 
to be measured. 

IHIVeremtiAl CtAlvAaometcir Metltod. — In galvanometers ha vine 
two coils wound side by side, separate currents sent through them in opposite 
directions exert a differential action on the movable system. In a differ- 
ential galvanometer the two coils are equal in their magnetic action on 
the movable system for equal currents, so that equal currents sent through 
them in opposite directions will not deflect the needle. If the currents 
' are unequal, then the deflection is a measure of their difference. Thia 
form of galvanometer may be used to measure resistanoe by inserting the 
unknown resistance in circuit with one coil of the galvanometer and a 
known adjustable resistanoe with the other, both circuits beins connected 
in multiple. Then when the resistanoe is adjusted imtil no deflection is 
produoea the resistances in the two circuits are equal. 

The method is often used in the comparison of the conductivity of wire, 
and where rapid measurements not requiring great accuracy are desired. 

W^lieatet4ni«*a JBrMfpe. — For accurate measurements of resistance 
the Wheatstone Bridge method is almost universaU:^^ used; Fig. 4 is a dia- 
gram of the connections in which a, 6, and R are 
known resistances and x the unknown resis- 
tance to be measured. O is the galvanometer, 
and fi is a battery of several cells, the number 
.4 of which may be varied according to the value 
of the resistance x. R is adjustM until there 
is no deflection of the galvanometer needle when 
both keys are dosed. 

The battery key should always be closed be- 
fore the galvanometer key is depressed or there 
will be a ^' kick " in the galvanometer due to the 
sdf inductance or capacity of the circuit under 
test. 




FiQ. 4. 



X h h 

When a balance is established - =-, or x = R -• 
. Ran 

Tlie resistances a and b are, in practice, made even multiples of 10, so 
that X can be read directly from R, the proper number of figures b^ni; 
pointed off decimally. 

If a = 6 the value of z is the same bb R, If x be sreater than the ca> 
pacity of R, or low in comparison to it, then a and 6 must be so chosen 
that their ratio respectively multiplies or divides R, 



For example, let 



6=1000 {then x = ". ft=^-^X 243 = 24,300. 
« = 243 ) « 



10 



The ratio of a to 6 being 100, any reading as ft is multiplied by 100, or 
again let 



a =1000 
6=10 
« = 243 



then X = 



10 
1000 



X 243 - 2.43. 



The ratio of a to 6 being r^. any reading as R should be divided by 100. 

A commercial form of Wheatstone Bridge of the Weston Model is shown 
diaKrammatically in Fig. 5. This type, called the "plug in" type, or some 
modification of it, is most commonly used. It has tne advantage over the 
'* plug out " type in that fewer plugs are required, there being but one 
plug needed for each decade; this reduces the plug error to a minimum. 



BESISTANCE HBASUBEMEKTS. 



67 



igr OlHMHieter. — Another form of instrument used 
for mtmmannf resistances is known as the direct reading ohmmeter. Briefly 
desc ri bed it is simply a slide wire bridp^e. the wire formins two of the arms 
of the bridce. a known resistance a third arm, and the unknown resistanee 



rH(i[iH 



^ B« 6- C13: 

HUNOS. TEMS UNITS R X 




c— — X — ^l..,l^. — 



T-_,I j- 



-SBa 



1 -P Qa P 



I X I 



1-^-i 



Fia. 6. 



tiie fourth. The shde wire is graduated to read directly in ohms, and is 
printed with niunbers in black and red. The black numbers refer to a bw 
reading scale which is used when the single plug of the instrument is fitted 
into tbe hole marked black, and the red numbers refer to a higher scale 




Fio.6. 



♦HI 



Fio.7. 



F%. 6 shows diagrammatically the oonneetions of this Ohmmeter, and Fig. 7 
gives Uie same ones expanded into the conventional Bridge Form. 



the plug is inserted in the hole marked red. This instrument usually 
kss four scales, although it is sometimes made with three and five. The 
Aie wire is doubled back on itself by means of a heavy cross block of 
practically sero resistance. 
The detector circuit comprises a detecting instrument ordinarily a tele- 
% and a stylus, which is touched at various points along the 



68 



MEASUREMENTS. 



slide wire until the detector by silence indicates a balance, when the resoit 
is read directly in ohms. In some of the instruments the battery is equipped 
with a small induction coil which provides alternating current. In this 
form the instrument is useful for meiisuring electrolytic resistance and 
other resistances containing electromotive forces that may be developed 
by the presence of current therein, and by the use of a suitable condenser 
in place of the known resistance, capacities can be compared. 

virectloBUi for Use of liar« Direct RoiMtUiir Oliii«ot«>r. — 
To Measure Resietance. Connect the terminals of the circuit to be measured 
to the posts, A and D. Place the telephone receiver to the ear and cloee 
the battery key, K, located in the receiver. Hold the stylus, <S, in the 
hand in the same manner as a pencil, and with it touch the straight wires 
along their entire length until a point is readied where gentW tapping the 
stylus on the wire produces no sound in the telephone. The resistance 
sought is then that indicated by the scale under that point of the wire. 
Dunng these readings the plug, P, must be in one of the sockets at the 
right-hand end of the rubber cross-bar. When in the socket marked "red" 
the scale numerals printed in red should be used. When in the socket 
marked "blue" the blue numbers should be read, etc. 
Slide-wire Sridflr** — A very convenient form of bridge for ordinary 

use where extreme accuracy is not de- 
manded is the slide-wire bridge, shown in 
Fig. 8. It consists of a wire 1 meter long 
and about 1.5 mm. diameter stretched 
parallel with a meter scale divided into 
millimeters. A contact key is so arranged 
.as to be moved along the wire ao that 
contact with it can be made at any 
point. 

A known resistance R is connected as 
shown; x is the unknow^n re8i8ta.nce; the 
PiQ. 3, galvanometer and the battery are con- 

nected as shown in the figure; atter closing 
the key Art the contact 3 is then moved 
along the wire until the galvanometer needle returns to zero; 




then again; 
and 



a : b :: R i x^ 

bR 

x = 

a 



The C»rey-Foater IVIetbod. — For the very precise comparison of 

nearly equal resiKtances of from 1 to 100 uhms this method yields exquisite 
results. In Fig. 9, Si an<l .S'2 represent the two 
nearly equal resistances to be compared, and Ri, 
R2 represent nearly equal rei^istances, which, for 
best results, shouUl not differ much in magnitude 
from iS, and S2. *^i and ^^2 s^^e connected by a 
slide wire whose resistance per unit length p is 
known. The battery and galvanometer are con- 
nected as in the diagram. A balance is obtained 
by moving the contact c along the stretchecl wire. 
Suppose the length of tlie wire on the left-hand 
side to the point of contact to be a units. Then 
exchange iSi ami S^ for each other without alter- 
ing any other connections in the circuit. Vpon 
producing a new balance, let oj be the length of 
wire to the left of the contact. 




Fio. 9. Carey-Foster 
Bridge. 



Then 



Siz=St+{a-aOp. 



. Special commutators are upon the market which have for their purpose 
the easy exchange of /?» and *S2. 

To avoid thermal effects, wliich arc nuite considerable with resistances 
made of some materials, the battery sliould be commutated for each pC'sition 
of the resistances to be compared. The readings for the two balances ac- 
companying the battery commutation shouUl l>e averaged. 



BESISTANCE MEASUREMENTS. 



69 



3K9mmur9m^0tmtm of JLow ]i«»Uitamce«« 



KelTla's ]»o«ble 
Bridge* — If a Wheatotone 
bridge be used to compare re- 
sistanoeB hftving a value much 
lesB than one ohm, the terminal 
and eontact resistances produce 
a considerable error in the re- 
sults. In conductorB having 
such low resist ance, the value 
of the resistajioe pven or to 
be measured is considered as ly- 
ing between two definite points. 
In standard resistances these 
points are connected to twoter- 




Fia. 10. Kelvin's Double Bridge. 



Biinals called potoitial terminals. ^ .,^ ... . «_. i_ ^. 

Kelvin has designed a modified form of Wheatstone bndge m which the 
above-mentioned errors are eliminated. The method is shown dii«rammati- 
cally in Fig. 10, in which R and x, the resistances to be compared, he between 
5 and Si on one and between T and Ti of the other, and are connected 
together at y; n and o are auxiliary resistances also adjustable. A galva- 
oometer is connected through a key, as shown, to two pomto. one at the 
junction of nand o; the other at the junction of a and o. If n and o be 
so adjusted that n:o::R:x, and a and b be adjusted so that the galvano- 
meter is balanced, then 

a :h : : R : x. 



or 



« = 



hR 



In practice, n and o may be changed during the adjustment of a and 6 
so as to maintain the ratio of n to o the same as that of a to 6, cither by 
ehanjqng n and o, on standard rheostats, or by opening the circuit at y 
sod adjusting n and o. as in a regular bridge, for a balanc^ after each trial 
value of a and b; then when a balance is obtained in the galvanometer 
with circuit at y both open and closed the above equation holds good. 

Amotiier Metliocl War Compfarlaon oflow JR«al«tances. — 
For comparing the resistances of ammeter shunts, etc., with standard side 
terminal resistances of the Reichsanstalt 
foam, the method of Sheldon yields 
rery accurate results. The unknown 
rodstance z. Fig. 11, which may be a»- 
ramed to be supplied with branch po- 
tential points a o, is connected bv heavy 
coodoctors in series with a standard re- 
sistance R, having potential points c d. 
From the two free terminals T T^ of 
these resistances are shunted two 10,000 
ohm resistance boxes S P, adjusted to 
the same normal temperature, and 
voond with wire of the same or negli- 
gable temperature coefficient, and con- 
nected in series. From the point of 
connection c, between the two boxes, connection is made to one terminal uf 
the galvanometer g, the other termhial being coimected successively with 
the potential points a, b, c, and d. At the outset all the plugs are removed 
from the box Sj and all are in place in the box P. After connecthig T and 
r» with a source of heavy current, plugs are transferred from one box to the 
eorresponding holes in the other box (this keeps the total resistance in the 
two boxes constant) until no deflection is observed in the galvanometer. 
This (Moeration is repeated for each of the potential points a, 6, c, and d. Bep- 
rsientlng the resistances in the box S on the occasion of each of these bal- 
ances by 5«, Sh, 5e, and Sd respectively, we h^ve the following expression 
for the value of the unknown resistance : 




Fig. 11. Precise Measurement. 



0? = 



Sa — Sb 
Se — Sd 



R. 



60 



MBASUBEMENT8. 



NoTK. — Mr. E. F. Northmp gives the following formula as handy in 
determining the percentage conductivity of metal wires. This oonductivitv 
is generally expressed as a certain per cent conductivity of Matthiessen^ 
stands^. To determine the conductivity, a resistance A of a sample is 
usually determined at a temperature 20^ C and of a length L From this 
measurement the pa* cent conductivity may be expressed as follows: 

i> * J *• * _ P X d X 100 

Percentage conductivity = ;g^ ^ IF X 581.054 ' 

where I = length in centimeters, W =r weight in grams, 

Am = resistance in ohms at 20^ 0, << = specific gravity. 

RKSKSTAlfCB OV AAKVAirOMBTBRft. 

When a second galvanometer is available, by far the most simple and sat^ 
isfaotorv method Is to measure the resistance of the galvanometer by any 
of the ordinary Whoatetone's bridge methods. Take the temperature at 
the same time, and, if the instrument has a delicate system, remove the 
needle and suspension. _ ^ . ^ , * i _• —1*1. 

Half Deflectton MeiMoA. —Connect the galvanometer in series with 

a resistance r and battery as in the following figure. 
^ Note the d^ection d ; then increase r so that the new 

>.JCr-VVVSAA-^ deflection d^ ^U ^ one-half the first, or | = d^ ; call 

Y^ J the new resistance r. ; then 

> ^ Resistance of Galvanometer = r. — 2 r. 

If the Instrument be a tangent galvanometer, then 
d and d| should represent the tazigents of the deflec- 
tions. 
Kelvin** Method. — Connect the galvano- 
meter, «s a; in a Wheatstone's bridge, as in Fig. 13. 
Adjust r until the deflection of C7 is the same, 
whether the key. is closed or oi>en. 

a 

The result is independent of the resistanoe of the 
battery. The battery should be connected from the 

1 unction of the two highest resistances to that of 
he two lowest. 

RKSISTAliCB OV BATTKRUBA. 

Goadeaaer Metlioa. — For this test is needed a condenser C, a balUstle 

galvanometer (7, a double contact key *», a resistance -R, 
of about the same magnitude as the supposed resistanoe 
of the battery B, and a single contact key k^. Connect as 
in the following figure. With the key k^ open, press the 
key *,, and observe the throw B^ in the galvanometer. 
Then, after the needle has come to rest, with key «, 
cloeed, repeat the operation observing the throw 9^ 
Then the resistance of the battery 



Fia. 12. 




Fia. 






x = R^' 



»i 




Fig. 



n««««^« IH»llectlon Mtetliod.-- Connect the 
battery B in circuit with a galvanometer G and a resist- 
ance r as in Fig. 16. Note the deflection d, and then in- ^^ . _ _^ 
^«Ma rto r. Sd note the smaller deflection d, ; then, if the defleetions of 
^^^ ' the galvanometer be proportional to the currents, 




_ r^di - rd 
^ - d-d^ 



-O. 



FlO. 15. 



If Tx is such that d^ = ^ , 



then 



i?=r,-(2r+flf>. 



BESISTAirCIt OF BODflB CIRCTTITS. 



61 



Tlie E JI.F. of the battery is supposed to remain unaltered during the 
messorement. 

MsBC«*s Heth«Ml. — Connect the battery as x 

la Wheatstone's bridge as in Fig. 16. Adjast r until 

the deflection of O Is the same whether the key be 

dosed or open. 

-^ h 

Tim £c-r-' 

a 

The galranometer should be plaoed between the ^*-«'^ 



pii 
lisl 



junction of the two highest resistances and that of 
the two lowest. 




Fig. 16. 



while W«rkt«c* — Connect the battery B 

alranometer 



Jtesuuuaee mm mwOMmirr wane ¥r •ricivr* — «Jounecv tne km 
with a resistanee r, and also m parallel with a eondenser C, jralrax 
6, snd key k \ shunt the battery through s with key A), as in FIk, 17. 

Close the key k, apd note the denectii 




ection d of 
the galvanometer, keeping X; closed, close kx and 
note du the deflection in the opposite direction. 
Then tne battery resistance 



B = s 



d^dx-^ 



dyt 



If r be large, the term -^ is negligible, and 



I Mag the multiplying power of the shunt. 



le M well tm ]»7H«Bsoa.— With 
djnamo or battery on open dircuit, take the Toltage across the terminals 
Tith a Toltmeter, and call it d ; take another reading d, at the same points 
vith the battery or dynamo working on a known resistance r : then the in- 

tvnal resistance B = "7 * r. 

In the ease of storage batteries, if the current / be read from an inserted 
immetar when charging, the resistance of the battery is 

2^ = ^. 



ad irtien discharging 



B = 



\mmTJLMCM ox* 



AMMKA^Ms JLEMMB OB HOVAB 

GMMGVITA. 



•oadni 




.—When the circuit has metallic return, it is 
ured by any of the Wheatstone's bridse methods, or, if the circuit 
can be supplied with current through an ammeter, then the full 

of potential across the ends of the con- 
ductor will give a measure of the resistance 
by ohms law, vis., 

_ . ^ drop in volts 

Resistance = — . — . 

current 

If the circuit has earth return as in tele- 
graph and some telephone cirei:dts, then 
place far end of the line to earth, and con- 
nect with bridge as in Fig. 18. 

Then the total resistance x of the line and 



Earth' 



Fte. 1& 



earth, is 



b 

x^r- 

a 



If a second line be available, the resistanee of the first line can be deter- 
■Uaed separated from tiiat of earth, as well as the resistance of earth. 



62 



MEASUREMENTS. 



Let 



r = resist&nce of first line, 
n = resistance of second line, 
rs = reisistance of earth. 



First connect the far end of r and rt tog^ether, and get the total reaistanoe 
R] connect r and r2> and measure the resistance Rg, connect ri and r^, and 
get total resistance R2, Then if 

— 2 

ri=T-Ru 
rt=T—R, 

This test is particularly applicable to finding the resistance of trolley 
wires, feeders, and track. 

For other methods for resistance measurements see under "Tests with 
Voltmeter." 



mSA/ilJRlilllE^T OF EM.ECTROinCO'MVS JPOHCE. 

Of Batt«rl««. — This can usually be measured closely enough for all 
practical purposes by a high class low-reading voltmeter (see Tests with a 
Voltmeter). 

lVli«atiitoiie'a lVKetlio«l. — Connect the cell or battery to be oompared 
in circuit with a galvanometer and high resistance r, and note the oefleo- 

tion^; then add another high resistance 



-/V^s/4'VN^ 



R., 







r* (about equal to r), and note the de- 
flection <ii. Next, connect the cell -with 
which the first is to be compared in cir- 
cuit with the galvanometer, and connect 
in resistance until the galvanometer 
deflection is the same as d; then add 
further resistance R until the galvano- 
meter deflection is the same as a, ; th«i, 
if e equals tlie E.M.F. of the first cell, 
and E equals the E.M.F. of the cell with 
which it IS compared, 



ri : R 



e 



E.. 



and 






Fio. 19. 



Or, the electromotive forces are pro- 

Sortional to the respective resistance 
eflection the same amount. 
Ijiiiiiii4eii*« ]iI«tli«Nl, — The two cells Ei and ^2 to be eompared are 

arranged as shown io Fig. 10. R^ and R^ are adjustable resistances which 
are large, as compared with the resistances of the cells. Ri and R^ are 
changed until the deflection in the galvanometer is reduced to lero. 



Then 



El _Rx 
Et - Rt 



If greater accuracy be required than that obtained by the above methods, 
some potentiometer method may be used, 
in which the cell to be measured is compared 
directly with a sttandard cell. 

Iiord Kajlelflrh'a Compcnaatlom 
IHethoil. — In the following diagram let 
R and Ry be two 10,000-ohm rheostats, B 
be the battery of larger E.M.F. than either 
of the cells to be compared, B| he one of the 
cells under test, G be a sensitive galvano- 
meter, HR be a high resistance to protect 
the standard cell, and k be a key. Obtain 
a balance, so that the galvanometer shows 
no deflection on closing the key k, by trans- 




FiQ. 20. 



MEASURING CAPACITY. 



63 



: fening reaiBtance from one box to the other, being careful to keep the sum 
of the resistance.? in the boxes equal to 10,000 ohms. Observe the resistance 
; ID R and call it R,. Repeat with the other cell ^21 ^^^ c&H ^he resistance 
I Rf. Then the CM.F.'s of the two cells 

Ei: Ei «- Ri: R^. 

Note. — Special boxes are on the market which automatically change the 
resistances R and Ri, maintaining the sum of the resistances constant, the 
vsiue of the resistance being read directly from the dials. 

Direct JtteiaJing' Pot«iitloBi«t«r. — There are many forms of po- 
tentiometers available, which are used in connection with a standard cell, 
And on which the potential difference to be measured is read directly from 
the switch dJalu of the instrument when it is balanced as shown by a gal- 
▼iDometer. Such potentiometers generally read to 1.5 volts. To meas- 
vc higher voltages than this a volt box must be used, which is simply a 
bigb resistance, across which the voltage to be measured is connected. 
C'ODnections are brought out from the resistance so as to include a known 
ponion of it. having such a value that the potential difference across it 
win be less than 1.5 volts. This is then measured on the potentiometer, 
ud the value found multiplied by the constant of the volt box. 

M«aaBr«»as«iiit of Current Uj Potentiometer. — The current to 
be measured is paf»ed through a standard low resistance, say, .01 or .001 
olun, and the mfference of potential across its potential terminals meas- 
ored by m^ins of a potentiometer. Then the current is by Ohm'a law 

R 

*here E is the difference of potential as measured, and R the reeistance 
«f ibe itandard. 



imAAVRiiiC} cAPAcionr. 

Arranyeniont of Condenaem. In Pnrallel. — Join like poles 

of the several condensers together as 
in the figure ; then, the loint capacity 
of the set is equal to the sum of the 
several capacity. 
Total capacity = c + C/ + <^// + <*//<• 
Condenacfra In Herlea. — Join 
the unlike poles as if connecting up 
battery cells in series as in Fig. 22, 
then tne joint capacity of all is the 




Fio. 21. 



rcetpfrocal of the sum of the reciprocals of the several capacities. 
Capacity C= ^ 



W.+^ 



+ ^ 



'// 



"/// 




Fia. 22. 



Capncltj' bj IMrect lliiicliarg«. — 

Charge a standard condenser, Fig. 23, ( « by 
» battery E for a certain time, say 30 sec- 
(4feis; then discharge it through a ballistic 
plFsnometer G ; note the throw d. 

X?xt charge the corideiiBer to be measured, 
^i, by the same battery and for the same leligth of time, and discharge this 
through the same galvanometer noting the throw d| ; 

Then C* : C\ :: e^ : d^. 

d. 




and 



C,= 



^ d 



For Kelvin's and Gott's methods see pages 326-^27, ** Cable 
Testing." 



64 MBASU&EMENTS. 

.Vrtdirv Metli«d. — For comparing the capacities of two oondenMn 
a and C, which are approximately the same, connect as in Fig. 94 thioiifl 
two rather high induotionless resistances 
i?i and R^ to the key k which makes and 
breaks contacts at each end. £ is a bat- 
tery. A galvanometer is inserted between 
the ends of the condensers where they 
Join the resistances. Adjust the resist- 
ances so that no deflection results when 
the key is manipulated. 

Then C=C,^. Fio. 24. 




»f PotoBtlAl Method. — The capacity of a condenser may b 

determined by the following formula: 

<^= — - — s 

2.303 R log - 

« 

where C is the electrostatic capacity, in microfarads, of a oondeneer^ thi 
potential of whose charge falls from E to e when it is discharged during ; 
seconds through a resistance of R megohms. 

If C is the known and R the unknown quantity, then 

R = —*- 



2.303 Jfc log- 

a 



In measuring the insulation resistance of a short cable by this method, thl 
discharge deflection E, compared with the discharge deflection obtained witi 
the same battery from a standard condenser, would give the value of h 
For long cables, however, this does not give correct results, and the ca- 
I>acity must be determined by other methods. 

H<SOT]tOHA«irCTIC Ilff]»UCTIOir. 

Xaw of iMdvotfoM. — When the magnetic induction or flux inter 
linked with an electrical circuit is changed in any manner, an ^ectr» 
motive force is induced in that circuit which is proportional in anK>unt U 
the rate of change of the flux, and acts in a direction which would, bg 
producing a current, tend to opxwse that change. 

Symbolically expressed the induced electromotive force in voits ia 

n d^ 

*"" 10" dr 

where ^ is the magnetic flux through the circuit, n the ntunber of tura 
of wire, and t the time. 

Self-induced electromotive forces are those induced in a circuit by changi 
in the current in the circuit itself. 

C4»efBcdemt of S«lf-IiSil action. — The practical unit of self-inductioi 
is the kenry, and is equal to 10* absolute units. 

The self-induction m henrya of any coil or circuit is equal numerically U 
the electromotive force in volts induced by a current in it changing at th( 
rate of one ami>ere per second. Thus the electromotive force in volte pre 
duoed in a circuit by a varying current is 

' = -^dt' 

vehere L is the self-induction in henryt and % the current hi 
If ^ = n, ^ represent the flux turns in the circuit, 

then ^ = Li X 10". 

For example, if a coil have 150 turns of wire, carrying a current of tv 



MEASUREMENT OF COEFFICIENT INDUCTION. 



65 



produeiiis 200.000 linea of force, or 200 kUoaHttMes through it, 
the flux turns equal 200,000 X 160 = 30,000.000. and the self-induotion is 
tbcrefore 

__ ^ _ 30,000,000 



L = ^S-. = 



lOH ~" 2 X 100,000,000 



= .15 henry. 



If the current of 2 amperes die out uniformly in one aeoond, then the 
deetromottve force induced is 

e= L ^ = .16 X 2 = .30 rolt. 






L = 



10» 



wlicn the permeability is unity. 
Where » = total number of turns of wire, 

n* = number of turns per centimeter length, 

A = area of cross section of solenoid. 
For mscnetic substances the above equation muat be multiplied by Mi the 
permeability of the medium. 



laiemta •€ Tke Coefldemt •€ MmAmeH^m, 



wlOi 



Caimcity. — The coefficient of self- 





Fig. 25. 



Fio. 26. 



iaduetion majr be determined by means of a Wheatstone bridge as follows: 
Let A and B, in Fi^. 25, be the bridge ratio arms, Rt the adjustable rheostat. 
Cooneet the ciromt to be measured as RL in series with a variable 
BoD-iadufltive resistanoe r and n a portion of which rt is shunted by a 
<Mda rd condenser of capacitj^ C. First balance the bridge for steady 
evrents by adjusting Rj,t that is, when the key K is closed continuously. 
"ten alter the proportion of non-inductive resistance ri, shunting the 
Modenser until no deflection occurs in the galvanometer when the key K 
■ open and dosed. Then the self-inductance 

Cvtmpmwimmm iHrith Kaown ••If-InducteMce. — Arrange in form 
of bridge as shown in Fig. 26, L being the imknown and Li the standard self- 
iadiKianee. Adjustable non-inductive resistances are connected in series 
«ith them. Call the resistances in each arm R and Rt, A and B are non- 
iBdnetive resistances. First adjust to a balance for steadv currents by 
rttsnging R and Ri, then adjust A and B until no throw ot the galvano- 
juter is observed when the galvanometer key is closed before dosing the 
wtery key. Then B vad Ri must be again adjusted for steady currents. 



HBAS0KKUKNTH. 



^ 



!' A R 
Then ^=b = b; 

II t, be oat of Ayrton »nd 
Porry'i bdjiutable iit> n < Ur dj of 
•elf-mduetion (»m Fig. 27), than 
the brides can tw baJsand la the 
iHmt'^'' "■I' 'a' aUxly eumnt, 
ftoa [or tnuuieot auiTe&U by 
mryinctba mlf-induction stand- 

eoilfl woimd oti BMtioiu of ood- 
oeotrie ■pherica] mrfaoea. the in- 
nde CDS of which oui be rotated 
with refvenee to the outnde oDo, 
and thua their enefficicot of in- 
dufltion vuied without cha&rinc 
tbeir rerirtwice. The Hie u 
nilUhwiryB m 



, dwrei 



i to42 



-n the 



Fio. 37. Ayrton i 



of aitOTuliDa or r«pidly interrupted direct current for tiio bstt« 
■howa in Fi^. 2S. The p&rt oA ia & ilide wire wilh telephoae oont 
K\ the ML[-induetanc« L uid Li iire eonnected m in the prerioui □ 



iLli£«r]^ 
<f the above, which 
■le^o"e'ln pta?«' rS 
for ^iie bsttery, u 




MBA8UBEHBNT OF MUTUAL INDUCTANCE. 



67 



AlUrsatiiis eurrent, J7, and the same with oontinuous ourrcot, £|, and the 
reading oithe ammet^' with the latter, /. 



Th 



L- 



Vjg» - Ex^ 



2wnl 

If the rerifitance Ri be known, and the ammeter be suitable for use with 

am 




Fzo. 29. 
akernating currenta, the switch an d non-indu ctive resistance may be dis- 

poised with. We then have L — ~ — ^— ^ . where I* is the value of the 

altvoating eurrent. 

Note. — The resistance of the voltmeter must be high enough to render 
itB eurrent negligible as compared with that through the resistance Ri. 

MeaanreaieBt of BlHtiuil MndncteMce. 

Connect the two coils whose mutual inductance ia to be determined, 
fir^ in series and then in opposition to each other. The self-induction of 
escb combination is then measured by any suitable method. 
Let M » the mutual inductance between 
the two coils. 
L ■■ the self-inductance of one coil. 
L, "> the self-inductance of the other 

coil. 
L„ -■ the self-inductance of both coils 
in series. 
» the self -inductance of both coils 
in opposition. 
Then nnee L^, — 1/ 4- L/ -f 2 3f 
«ad L,„ - L -f i^/ - 2 Af . 

Thfon the coefficient of mutual inductance 
desired is 



-•<// 



M 



L„ - L 



m 



Gomparlaon wltls a Kmowb Ca- 

_ ici^. — Connect as shown in Fig. 30 
vhcre A and Z> are two coils wnose 




1 


• 


~" ' 


« 




umitif. 


J 



Fia. 30. 



Bnitoal inductance M is required. R 
■nd Rx Are two adjustable non-inductive resistances and C a standard 
condenser placed in shunt to R and R-t. Vary the resistances R and R^ 
ontil no deflection is observed en the galvanometer when the key is opened 
or Closed. Then the mutual inductance is 



68 



MEASUREMBKTS. 



Coi 



iriaoa witli Known Self-Induction bj IB 



iiMinaon wiui jft.nown neii-mnancvion oj .vndfre. — la 

this method the mutual inductance of two coils is compared with the known 
self-inductance of one of them. The coil whose self-inductance is known 

ia connected as i? in Fig. 31. The other 
coil is connected in the battery circuit with 
its magnetic circuit opposed to that of the 
other coil. Then by adjusting the other 
arms of the bridc^e to a balance for both 
steady and transient currents, as in the 
methods for self-inductanoe, the mutual 
inductance is 

M ^. 

r-f fi 

Anotlior lUetliod. — In order that a 
balance may be obtained without the incon- 
venience of trial and approximation as in 
the foregoing method, the batterv circuit 
may be shunted by non-inductive resistance as 8 shown in Fig. 32. The 
other connections are similar to those of the previous test. The bridge 
is first balanced for steady currents in the regular way by adjusting the 
resistances Ri, r, and ri, and then 8 is changed until no deflection occurs when 
the key is opened or closed. Then the mutual inductance is 




Fig. 31. 



Af-- 



LR^S 



(Ri + fl)6' + (R + r)«i 



Contpniiaon of Mntnal Indnctnni^ wltk Known Solf-Mn- 
iiactnnco of Anotltor Cotl. — Connections are made as shown in Fig. 
33. One of the two coils whose mutual inductance is to be measured ia oon- 




Flo. 32. 




Fig. 33. 



nected in the battery circuit, and the other in series with an adjustable 
non-inductive resistance as a shunt to the galvanometer. The known 
self-inductance L is connected in the bridge as A. The bridge is first 
balanced, as before, for steady current, then the resistance S is chaoged 
until no deflection occurs when the key is opened or closed. Then if iSTbe 
the total resistance in the shunt circuit, the mutual inductance is 

-- LiR\S 

M ■""" "777 



iR+Rx)* 

Volopliono nCetliod. — As in measurements of self-induotanoe, a tele- 
phone may be used in measurements of mutual inductance,^ as shown in 
Fig. 34. The coil of known self-inductance L is connected in one arm of 
the bridge, as shown at R. The other coil is connected in opposition 
to that coil in the main current circuit, the current supplied being either 
alternating or a rapidlv interrupted direct current. The non-inductive 
resistance and the telephone circuit contact are varied until silence occurs 
in the telephone in a manner similar to that described for self-inductance. 



MEASUBKMENT OF A.C. POWEU. 



69 



^ 



Then if p is the resistance of the slide wire for unit length, and the position 
for a baknce is a units from the right as shown, then the mutual inductance 



M -- 



Lap 



____ jter. — In measurements of inductance, when balancing for 
transient currents the galvanometer deflects in one direction when the 
bettery key is dosed, and in the opposite direction when it is opened. To 
increase the sensibility of such tests, Ayrton and Perry have devised the 
■eeohmmetcr. The battery and galvanometer circuits are each commuted 





Flo. 34. Fio. 35. Ayrton and Perry's 

Secohmmeter. 

■0 18 to prodttce a galvanometer deflection in one direction, and increased 
ia amount. This apparatus may be used in connection with any of the 
above testa where ^Ivanometers are used, the balance being obtained 
when the deflection is reduced to aero. Below is given a description of the 
apparatus as shown in Fig. 35. 

This instrument serves the purpose of making an alternating current to 
on in measurements of self-iiKluction, and of commuting such portion of 
tfait current as flows in the galvanometer circuit to a direct current. 

The instrument consists of two rotating commutators mounted on one 
axii and a train of gears for rapidly driving them. The commutators are 
oa the two sides of a cast metal case, one only being shown in the illustration. 
They are electrically insulated from each other. The brushes of one com- 
mntator are mounted on a disk, which can be rotated through an angle of 
90* a round the axis. The brushes can accordingly be set so that they will 
KTcrse the circuits in which they are connect^ at the same time, or so 
that one will reverse at any desired fraction of a period after the other. 
The driinng handle may be attached at two places on the train of gears, 
thv pving two speeds. A pulley wheel is also provided', which may be 
used m place of the handle and the apparatus be driven by a motor. 

MMJkSmMMXmwm of POUnER Iir AI^VlSRIf ATIIf« 

CimitBira GXRC17IT0. 

In alternating current circuits having inductance in any part of the cir- 
cuit, such as motors, unloaded transformers, and the self-inductance of the 
line itsdf, the product of the values of the current and the E.M.F. as shown 
by an ammeter and voltmeter does not give the power in the circuit, 
niee the current is not in phase with the E.M.F. 

The power at any instant of time in any alternating current circuit is 
eooal to the product of the instantaneous values of the current and E.M.F. 
This is shown graphically in (Cut A) Fig. 36. The mean power in the circuit is 

P ''EI, 
vhere B is the effective E.M.F. and / the effective current. The effective 
nlueB of E.11.F. and current are the square roots of the mean squares of 
their respective instantaneous values, or numerically, their maximum 

Tdoee divided by V2 or 1.41. Alternating current measurinia; instruments 
of either the "hot wire" or dynamometer type indicate effective values. 
If the current is not in phase with the E.M.F., 



m phase is ^, then the power is 

P - J?/ cos ^ 



and the angular difference 



70 



MEASUREMENTS. 



n 


\7 







/. 



* / 



^y 



.^' 



Fio. A. 




Fig. B. 



-7^ 




'1 2/'' 



Fro. C. 




Pio. D. 




Fxa. £. 
Fio. 80. 



^ 



M£A8UH£M£NT OF A.C. POWBB. 71 



Cm ^ is oan«d the power factor, since it \b the factor by whioh the apparent 
power BI must be multiplied to obtain the true power. 

Suppose that curve No. 1 in Fig. B, page 70, represents the various values 
of the impressed voltage throughout a cycle, and that curve No. 2 represents 
tbe various values ofthe self-induced voltage. Curve No. 2, it will be noted, 
if not in phase with curve No. 1. Its highest value comes at a later time 
than that of curve No. 1, because the self-induced electromotive force it 
never in phase with the impressed electromotive force, as the self-induced 
eleetromotive force is obviously at its highest point when the lines of force 
induMd by the coil are changin|[ P?*^. "^pidly. This occurs when the 
cuiTCDt is rapidly increasing or dimimdbing, and not when it is maintain- 
ing a momentarily steady value at its highest point. 

Current will flow in the circuit in proportion to, and in phase with, the 
resultant of the two curves, and the ordinates of this resultant will be the 
&||ebnucal sum of the corresponding ordinate of the two curves. Curve No. 
3du>ws the resultant curve constructed in this way. It will be found to be 
amilar to the other curves but of a different maximum value, also lagging 
behind the curve of impressed E.M.F., but occurring earlier than the curve 
of aetf-indueed E.M.F. 

la fig. C are shown the curves r^resenting the impressed E.M.F. and 
the resulting current, and as will be seen the current lags behind. If 
the values of these curves be combined by multiplying them toi^etha*. 
ordinate by ordinate, this curve representing power will result. This will 
be the true curve of power, as it obviously represents the power at every 
instant, the instantaneous voltage being multiplied by the instantaneous 
current, and eonsequently takes account of the fact that th«r maxima 
■re shifted with reference to one another. 

If the current and voltage curves are arranged as shown in Fig. D. in 
wbidi the maximum value of the voltage occurs at the same time as does 
the minimum value of the current, the result will be as shown, and no 
power will be produced. 

If the current is in phase with the electromotive force as shown in 
Fig. £, the power curve will appear above the aero line, and the true 
power will also be the apparent power. 

'WMw Voltatetcr Method. JLyrtmwt * flvaipMcr. 




This method ie good where the voltage can be regulated to suit the load. 

In figure 37 let the non-inductive re- 
sistance B be placed In series with the 
load a b ; take the voltage V across the 
terminals of Ji\ Vx across the load a 6, 
and V^ across both, or from a to c. 

Then the 

True watts = — ? — . 

Fio. 37. The best conditions are when V = Tj, 

and, itR=:\ ohm, 

then ir= r,«— Ki«— F». 

C«aiMn«d Vol«M«ter and Ammeter TUmt^mtL 

Hiis method, devised also by Fleming, is quite accurate, and enables the 

accuracy of instruments In use to be 
checked. In Fig. 38 A Is a non-inductive 
resistance connected in shunt to the Induc- 
tive load a 6, and the voltmeter V mesAures 
the p. d. across xy. A and A^ are ammeters 
connected as shown ; then 




True watts = ^ (a,* -A*-(^)^. 



Fig. 38. If the voltmeter F takes an appreciable 

amount of current, It may be tested as fol- 
towii : disconnect R and V at y, and see that A and A. are alike ; then con- 
Met R and K at tf again, and disconnect the load a h. Then Ai = current 
taken trr Jt and Fin multiple. 



72 



ME AS UREMENTS. 



WA!rrMKVKIt METHOIMi. 

(Contributed by W. N. Goodwin, Jr.) 

For meaaurement of power in electric circuits, the wattmeter eivee the 
ciiiickest and most accurate reeults. Since the instruxnent mechanically 
integrates the products of the instantaneous values of current and E.M.F., 
the power is indicated directly, regardless of the power factor. 

When a wattmeter is coimectM to a circuit, the instnunoit itself re- 
quires current and. therefore, some power is consumed in it. This error 
must be calculated and subtracted from the observed readings. Weston 
wattmeters are compensated for this error by means of a ooil wound in 
opposition to the field coil and adjusted with it. The following are a few 
of the important tests with a wattmeter used in power measurements. 

Fig. 30 shows the connections for measurement of power in either m 
direct or single phase alternating-current circuit. The power oonsumed 
by L is read directly from the instrument. 





Fio. 39. 



Fxo. 40. 



In direct current measurements, to eliminate the effect of the earth's 
magnetic field, two readings must be taken; either the connections must 
be reversed for the second reading, or the instrument turned 180^ from its 
first position; the mean bf the two readings gives the true power. 

If the instrument have a multiplier, it should be connected as shown in 
Fig 40j so that the difference of potential between the stationary and mov- 
able coils shall be a minimum. 

Clieoktii^ IVattmeters. — In checking wattmeters either directly with 
other wattmeters, or by means of a voltmeter and ammeter, the wattmeter 
should be connected so as not to include its compensating ooil. In a Wes- 
ton wattmeter the "independent" landing post should be used, shown in 
Fig 30, the pressure circuits being connected in parallel and the field or 
current coils in series. 

Hire«i«PluMe Power llleasiireiiiente. — In unbalanced systems 
two wattmeters are required, connected as shown in Fig. 41 . llie totalpower 
transmitted is then the algebraic sum of the readings of the two watt- 
meters. If the power foctor is greater than .50^ the power is the arith- 
metical sum, and if it is less than .50, the power is the arithmetical differ- 
ence of the readings. 




Fio. 41. 



WATTMBTER METHODS. 



73 



Xterce^y fcwc •TNteaui. — One wattmeter may be used 
in three-phase circuits in which tne current lag is the same for all parts 
of the circttit and the load is uniformhr distributed. The connections are 
ihown in Fi|^ 42. The current coil oi the wattmeter is connected in one 



Tb 




J^ 



■•'NXWV^ 



FiQ. 42. 



of the leads as A; one end of the pressure circuit to the same lead, the other 
end is connected successively to each of the other leads as B and C, a read- 
ioK bains taken in each position. The i>ower is then the sum of the sepa- 
rate readings. 

•ecMM JHKetkod f«r Jtoliaitced Ctrcnlte. — Another method may 
be and by which the power may be obtained from a single reading of the 
iiatnunenti as shown in Fig. 43. The current coil of the wattmeter is 
eonneeted in one lead as A; one end of the pressure circuit is connected 
to the same lead. 




FiQ. 43. 



The other end of the pressure circuit is connected to the junction of 
two renstances r and r, each equal in resistance to that of the wattmeter; 
tbe ends of these resistances are connected to the other two leads as 
■bown at B and C. llxe power is then 

P = 3p 

wfwre p ii the instrument reading. 

If it be desired to use the instrument for higher voltages than that for 
viueh it was designed, then a resistance R must be added to the instru- 

i2 -f- r 
mnt branch, of such a value that — ■ — is equal to the multiplying con- 
stat m desired. 

Each of the other two branches must be increased to B-^r, 

Then the power is 

P = 3 mp. 

The Weston *' Y box" multiplier, which may be made for any multiplsong 
motant, is constructed according to this principle. 

Any of the above methods can be used equally well for the delta as for 
UMstiir oonnection. 



74 



MEASUREMENTS. 



The following are a few of the more important testa for which Toltmetcn 
and ammeters are especially adapted. With some changes and additions 
they have mostly been condensed from an article by H. Maschke, Ph.D., 
of the Western Laboratory published in the Electrical World in April, 1S92. 

The scales of the better known portable instruments read, in general, 
from to IGO, or some even multiple or fraction of this value. Voltmeters 
are available having scales rannng from 1.5 volts to 750 volts for a fall 
scale deflection, and when used with multipliers for any higher ranee. 
Two or more ranges may be had on the same mstrument, so that by mmply 
transferring connections from one binding post to another, voltaces aif- 
fering greatlv in amount may be measured on one instrument. Millivolt- 
meters may be had reading as low as 20 millivolts for a full scale deflection. 

InatnuBenta wltb PermMsent Ma^rnete should not be placed on 
or near the field magnets of motors or generators, nor should they be used 
for measurements in very strong magnetic fidds, such as those produced 
in the vicinity of conductors carrying heavy currents. If the fields be 
not too strong, then the error produced in the instrument from this cause 
may be eliminated by taking the mean of two readings, one in position, 
andf the other when the instrument is turned 180^ from that position aroona 
its vertical axis. 




Slectroatotlve Farce of IBatteiiea. 



The positive post of voltmeters is 
usually at the right, and marked +• 
In a battery the sine is commonly neg- 
ative, and should therefore be con- 
nected to the left or negative binding 
post. 

For single cells or a small number, 
a low-reading voltmeter, say one read- 
ing to 15 volts, will be used, the con- 
nections being as per diagrams. 



Klectromotlve 
of 



WiUJUHh 




For voltage within range of the instrument available for the purpose. It ia 
only necessary to connect one terminal of the voltmeter to a brush of one 
polaritv, and the other terminal to a brush of the opposite polarity, and 
read direct from the scale of the instrument. As continuous current volt- 
meters usually deflect forward or back according to which pole is connected^ 
It is necessary sometimes to reverse the lead wires, in which case the polar- 
ity of the dynamo is also determined. Of course the voltage across any cir- 
cuit may be taken in the same way, or the dvnamo voltage may be taken at 
the switchboard, in which case the drop In the leads sometimes enters into 
the calculations. Following are diagrams of the connections to bipolar and 
multipolar dynamos : 





PlO. 46. 



Fio. 47. 



TESTS WITH A VOLTMETER. 



76 



In fhe eaae of arc dynaxnoe or other machines giving hish voltage, It is 
necessary to provide a multiplier in order to make use of the ordinary in- 
strument ; and the following is the rule for determining the resistance 
Yhich, when placed in series with the voltmeter, will provide the necessary 
raoltiplying power. 

Lst e = upper limit of instrument scale, for example 150 volte, 

E = upper limit of scale required, for example 760 volts, 
R = resistance of the voltmeter, for example 18,000 ohms, 
r = additionid resistance required, in ohms. 



Then 



r==Ji^-J5orr==18/)Oo5?^gJ!5? =72,000ohms. 

J? TfiO 

The multiplying power = — or -^^ = S. 



Should the exact resistance not he availahle, then with any available 
mistaooe r^ the regular scale readings must be multiplied by ( ^ + I ] • 

of Hlrli BeaiateBce for Volta 




5 .-A/WVsA/VA— A 



It is highly important, as reducing the error In measurement, that the in- 
ternal resistance of a voltmeter be as high as practicable, as is shpwn in the 
following example : 

Let £ in the figure be a dynamo, battery, or other 
KKiroe of electric energy, sending current through the 
reHBtance r; and vm. be a voltmeter indicating the 
pneeore in volts between the terminals A and B. Be- 
fore the vtn. is connected to the terminals A and B there 
will be a certain difference of potential, which will be 
kas when the voltmeter is connected, owing to the les- 
Beniiig of the total resistajice between the two points : 
if the resistance of the vm. be high, this difference will 
be Tery small, and the higher it is the less the error. 
Following are the formulas and computations for de- 
tenaining the error. 

In Fig. 48 let £ be the E.M.F. of the generator, 
r the resistance of the circuit across A and B when 
the difference of potential is to be measured, Vx the 

raistance of the Mads, generator, etc., and R the remstance of the volt- 
Bicter. Before the vm. is connected the diflerence of potential between 
AaodBis „ 

r + rj 

With the roltmeter connected the difiference of potential indicated by 
the instrument is 

V,- 




Fio. 48. 



rRE 



tR + Tir + TxR 

The voltage aeroes A and B is, therefore, reduced by the introduction 

*ie amount of 

rvxVx 



(tf the voltmeter by the amount of 

V-Vx 
The error is 



{X'\-rx)R 



100 



(^) 



lOOrr, 



U 



Vx / (r-f ri)ft 

The error is inversely proportional to the resistanoe R of the yoltmeter. 

Example : 

E "10 volts, 
r — 10 ohms, 
ri *- 2 ohms, 
R — 500 ohms. 

IhsQ the reading of the voltmeter is 

„ 10 X 500 X 10 n -rtRft ^^u- 

^'" (10 X500)-K2 Xl0 ) + (2 X500)"^-^^^^'*^ 



76 

and the error ia 



MEASUREMENTS. 



y _ K. - ^^4441^ - .0277 volt.. 



and the percentage error is 

P = 



(10 + 2) 600 
100 X 10 X 2 



aO-f 2) X600 
If R be made 1000 ohma. then 

,, 10 X 1000 X 10 

\ ^ mm 



-.333%. 



and the error is 

and the percentage error is 



(10 X 1000) + (2 X 10) + (2 X 1000) 



— 8.32 volU 



V^ -V - ^?.^^,^J^,^^?? - .01387 



P - 



(10 4- 2) 1000 
100 X 10 X 2 



- .166% 



(10 + 2) X 1000 

or just one-half the error with R — 5(X) ohms. 

If the error of measurement is not to exceed a stated per cent p, then r 

an:i ri must be such that n 

I * is less than :^- 
r-j-ri 1(X) 

If the circuit is closed by a resistance ri, and it be deared to measure 
the E.M.F. of the generator by connecting the voltmeter between any 

two points as A and B, then E '^ ( — ^^— * ) Vi, where Vi — reading on rm. 

The error between the true value of the E.M.F. of the generator and that 
shown by the voltmeter is t^ 



{^ 



R 



and the percentage error p °« 100 

If the error is not to exceed p per cent, then the resistance of the gen- 
erator, cables, etc., must not exceed -—z- 

For example, with a voltmeter having 15,000 ohms for 150 volts; if p 

— 30 ohms. 



must be less than i%, then r^ may be fts great as 



i X 15000 
100 



CoBip»riiiOM of IRJIK.V, of liatterltw. 

l«'h«at)iitoii^*ii lUethfid. — To compare E.M.F. of two batteries. A and 
X, with low-reading voltmeters, let £ be the E.M.F. of A, and E\ the E.M.F. 
of X. 



■V^/W^AAAAA^ 




Fxo. 40. 



First oonneot battery A in series with the voltmeter and a resistance r, 
switch B being closed, and note the deflection K; then open the switch B^ 
and throw in the resistance r^ and note the deflection T,. Now connect bat- 
tery X In place of A^ and close the switch 5, and vary tne resistance r until 
the same deflection Fof voltmeter is obtained and call the new resistance r. ; 
next open the switch B, or otherwise add to the resistance r, until the deflec- 
tion f\ of the voltmeter is produced ; cull this added resistance r„ then 

E -.Ex ::r, :r,. 

If E be smaller than i^,, the voltmeter resistance R may be taken as r, and 
it is better to have r^ about twice as large as the combined resistance of r 
and the resistance of A. 

It is not necessary that the Internal reBistance of the cells be small as 
compared with R. 



^ 



TB8XS WITH A VOLTMETER. 



77 



PonremdorlTB MetMoA HodUlcA by Clark. 

Ite Compare the EJtf .F. of a battery cell or element "with a standard oelL 
Let i9 be a standard cell, 

7* be a cell for comparison -with the standard, 
^ be a battery of hfsher E.M.F. than either of the above elements. 
A reaistaaee r ts joined in series with the battery B and a slide wire A D, 
A mflllToltmeter is connected as shown, both its terminals being oonnected 
to the like poles of the battery B and the Standard S. 




Fig. go. 



MoTe the contact C along the wire nntil the pointer of the instnunent 
ituids at zero, and let r^ be the resistance of A C. 

Throw the switch 6 so as to cut out the standard S^ and cut in the cell T\ 
now slide the contact d alons the wire until the pointer again stands at 
SHO, and call the reelstance oi ^ <7i r,, 

Then the £.M.Fb. of the two cells 

T: S ::r, : r,. 

If a meter bridge or other scaled wire be used in place of A 2>, the results 
nay be read directly In yolts by arranging the resistance r so that with the 
pointer at zero the contact C is at the point 144 on the wire scale, or at 100 
tim«8 the E.M.F. of the standard 8, which may be supposed to be a Clark 
«eQ. All other readings will in this case be in hundredths of volts ; and 
dwald the location of Cx be at 175 on the scale when the pointer is at zero 
mlhemllliToltmeter then the E.M.F of the cell, being compared, will be 

LISTOltS. 

MMksvrlaff Curr«Bit fitr«Mr<b witli i» Voltmeter. 

H the resistance of a part of an electric circuit be known, takine the drop 
la potential around such resistance -will determine the current flowing by 

ohms law viz., /= -^ . 

In the figure let r be a known resistance be- 
tvwD the points A and B of the circuit, and / 
fteitrengtn of current to be determined ; then 
if tiie Toltmeter, connected as shown, gives a 
MtftjiTn of V volts, the current flowing in r 

viUbe 




r 



For the corrections to be applied in certain 
ciMs, see the section on Importance of High 
BaUbuux for VoUmeters. page 75. 

Always see that the reelstance r has enough 
eurying capacity to avoid a rise of temperature 
vfaieh -woold change its resistance. 

If the reading is exact to — volt the meas- 

^ 1 

srement of current will be exact to z-rr^ *™- 



ff WVS/WNA/WNAAA* 00 




FlQ. 51. 



78 MEASUREMENTS. 



peres. Ji r^JH ohm, and the readings are taken on a low-reading volt- 
meter, say ranging from to 5 volts, and thai can be read to sio volt, thea 
the possible error will be 

300XT *" fso '"P*'*- 
If rbe made equal to 1 ohm, then the volts read also mean amperes. 

]IIeaa«v«Hi«Bt •€* Cvrreat with m HlllllT^ltiii^ter. — This ia the 
method generally used in practice for the measurements of currents, and 
is the same principle as the one outlined above with the substitution of a 
millivoltmeter for the voltmeter. 

As the drop is much lower, a comparatively low resistance shunt may 
be used, so that heavy currenta mjfty be measured without thediunt becom- 
ing disfH'oportionately large. 

For portable instruments, detachable shunts are generally adjusted with 
the instrument so that the instrument scale reads directly in amperes, llie 
shunts are constructed of resistance alloy having a negligible temperature 
ooeflScient. 

Switchboard instruments also have shunts with slotted terminals ao 
that they may be connected directly to the bus-bars. 

In some cases where the currents to be measured are very large the in- 
struments are adjusted to the drop across a portion of the copper bus-bar 
through which the current passes. To compute the leni^th of the copper 
bar of a given cross section to give a certain drop for a given current, 

let i4 » the area of the cross section of bar in square inches, 

/ — current in amperes, 
V ■■ drop in millivolts desired for instrument for current I; 

then, length in feet - ^^ ^ "^ at 20" C. 

HteaaviiMiT nealateMoe witli » Voltmeter. 

d«ii«Tml Metlioda. — In the figure, let X = the unknown reeistance 
that is to be measured, r = a known resistance, E, the dynamo or other 

steady source of E.M.F. 
f. When connected as shown In the figure, let 

the voltmeter reading be V ; then connect the 
voltmeter terminals to r in the same manner 
and let the reading be F^ ; then 

X:r::F:Fi 

and X = '^. 

If, for instance, r = 2 ohms and F = 3 volta 
and Fj = 4 volts then 



X 

— VNAAAAAr 




'A/^NSr-^ 



Vm, 

FlO. 62. 



ji:=?^= 1.5 Ohms. 

If readings can be made to ^ volt, the error of resistance measuremant 
will then be P 



100 X J- 1^^+ jrj per cent. 

and for the above example would be 

1 (i + J) = 0.68%. 

Should there be a considerable difference between the magnitudes of the 
two resistances X and r. it might be better to read the drop across one of 
them from one scale, and to read the drop across the other on a lower scale. 

Re«tataBc« HIeaaiir«ai«iit witM Voltmeter and Ammeter. 



The most common modification of the above method is to insert an am- 
meter in place of the resistance r in the last figure, in which case X=z-f 
where / is the current flowing In amperes as read from the ammeter. 



TESTS WITH A VOLTMETBB. 



79 



If tfae readings of the roltmeter be correct to — and the ammeter read- 

P 
ings be correct to the same degree, the possible error becomes : 

100 Xj ( ^ + i) per cent. 



lest of T^wy AnuUl 



ilstancea witli 



a MUltTolt- 



By using a milUyoltmeter In connection with an ammeter, Tery small re- 
fistances, such aa that of bars of copper, armature resistance, etc., can be 
ftccnrately measured. 




sio.6a 



In order to have a reas- 
onable de^ee of accuracy 
in measuring resistance by 
the " drop" method, as this 
is called, it Is necessary 
that as heayy currents as 
may be available be used. 
Then, if iP be the dynamo 
or other source of steady 
E.M.F., X be the required 
resistance of a portion of 
the bar, V be the drop 
in potential between the 
points a and 6, and / be 
the current flowins in the 
circuit as indicatea by the 
ammeter, then 



lbs applications of this method are endless, and but a few, to which it is 
ttpedally adapted, need be mentioned here. They are the resistance of 
armatures, the drop being taken from opposite commutator bars and not 
from the brush-holders, as then the brush-contact resistance is taken in : the 
ratfttsuice of station instruments and all switchboard appliances, sucn as 
tbe resistance of switch contacts ; the resistance of bonded Jotuts on electric 
nOway work, as described in the chapter on railway testing. 

mm 



irenseat of Hlfli IleaiateBcea. 

WiUi the ordinary voltmeter of high internal resistance, let R be the re- 
Bstance of the voltmet^*, X be the resistance to oe measuredi. Connect them 
ap fai series with some source of electro- 
aotiye force as in the foUowins figure. 

Cloee the switch 6, and read tne voltage 
r vith the resistance of the voltmeter 
thne in drcuit; then open the switch, 
Uioi cutting in the resistance X, and take 
ttofher reMing of the voltmeter, V,, 



Tta X=b{^-i). 




FlO. 64. 



If the readings of the voltmeter be cor- 
rect to - of a volt the error of the above 
p 

nnltwiUbelODx-jr ( y"^ p ) percent. 

Vef7 Higrii nealatWBce. — For the measurement of very high resis- 
tsDCSB a more sensitive voltmeter will give much bett^- results for the reason 
thst the reading Vi when the switch h is opened, becomes so small with the 
ordhiary voltmeter that the error is relatively very great. Instruments are 
<m the market having a sensibility of 1600 ohms per volt or about 260,000 
ohPH for 150 volts. 



80 



MBASUREMENTS. 



For example if x — 1 mesphm and an ordinary voltmflier be used 
R ^ 15,0(X> ohms for 150 volts, 
and Z — 120 volts. 

ER 120X15.000 . 1.772 Tolta; 



whUeif 



Vt would be j^ _j_ ^ 1 ,000,000 + 15,000 
R were 250,000 ohms. 

120 X 250,000 



Vi would be 



» 24 volts. 



1,000.000 + 250.000 

that is with the high resistanoe instrument, with the same aoearaey of 
the instrument soales, the percentage error is about ^ as great as with the 
lower resistanoe instrument. 

Meaavrteg' tlie Mnaulatloa SeeiatAiic« of lAtflMUmtr wtmd. 
Power Clrcvita wltli m Voltmeter. — For the measurement of in- 
sulation resistance, a high resistance sensitive voltmeter is needed. For 
rough measurements where the exact insulation resistanoe is not reauired 
but it is widied to determine if such resistance exceeds some stated figiure, 
then a voltmeter of ordinary sensibility will answer. The methods in general 
are as follows : 

Let X ■• insulation resistance to ground as in Fi|(. 55, 
Xi » insulation resistanoe to ground of opposite lead, 
R — resistance of voltmeter, 
V — potential of dynamo E, 
Vt -> reading of voltmeter, as connected in figure, 
Vi ■• reading of voltmeter, when connected to opposite lead. 





Fig. 66. 




"^" AfVlfMl 



Then 



and 






The above formula can be modified to give results more nearly eon«et by 
taking into account the fact that the path through the resistance R of the 
voltmeter is in parallel with the leak to ground on the side to which it to 
connected as shown in the following figure : 




"^Ground 
FlO. 66. 



Ground "^ 



TE8T8 WITH A VOLTMETER. 



81 



1 



In tUa ease the Toltage V of the circuit will not only send current through 
the lamps, but through the leaks ef to ground, and through the ground to 
d and c, thenoe through 4 to 6, and c to a, these two last paths being In par- 
allel, therefore harlng less resistance than if one alone was used ; thus if r 
he the resistaaee of the ground leak b d^ and rj be the resistance of the leak 
f /• aad JK be the reslstanoe of the yoltmeter, then the total resistance by 
way of the ground, between the conductors, would be 

i2-|-r + *^»» 

F= Toltage of the circuit, 
V =r reading of roltmeter from a to 0, 
V, = reading of roltmeter from gtoe. 



=«( 



r-(»+r,) 



)• 



Thesum of the resistance r + r^ will be = JS 



( 






) 



Seel«tsft»c« of Are IilrM Ctac«lt«. 

Are lamps are to a great extent run in series, and the Insulation resis- 
taaee ot their circuits is found in a manner similiar to that for multiple 
cfanrits, hut the formula differs a little. Let the following figure be a 
tnieal are cfrenit, with a partial ground at c. 

ttast fliid the total Toltage K between a and b of the circuit. This can 
WMt handily be done with a voltmeter having a high resistance in a sepa- 
Bte box and so calibrated with the yoltmeter as to multiply its readings l>y 




FlQ. 67* 



eomreniMtt number. For oonrenience in locating the ground, set the 
voile per lamp by dividing the total Tolts V by the number of lamps 
M the drevit ; the writer haa found 48 volts to be a good average for the 
flidtavy 10 ampere lamp. With the 16 lamps shown in the above figure, V 
eeeU probably be about 768 volts. 

Sest take a voltmeter reading from each -end of the circuit to ground. 
Can the reading from a to ground v, and from b to ground v,^ R b^g the 
s ot roltmeter as before, and r the insulation resistance required. 



.=.( 






)• 



; the location of the ground, provided there be but one and the jB^eneral 

of the circuit be good, will be found closely proportional to the 

V aad V/ ; In the aoove figure say we find tne voltmeter reading 

frail 0*10 gronnd to be 38, and from b to ground to be 36 ; then the distance 

•< the gnMBd e tnmk the two ends of the circuit will be in proportion to the 

nadtagi S8 and m respeetirely. 

Itee being 16 lamps on the oironlt, the number of lamps between a and c 



82 



UEASVREMES TS. 



^°?^oJ^ ^.•^-^"♦"2^ = M of 16 = 7, «nd from 6 to c would be 36-^ 
(28 + 36) = If of 16 = 9 ; that la, the ground would most Ukely be found be- 
tween the Beventh and eighth lampe, counting from a. 

lBs«]»tlo» acr«M a Doable Pol« Fane Block or Otker 
Similar Bevico wfeiero Botk TonMiaalii are on 

tihe Same liaeo. 

Let// be fuses in place on a base, 

V = potential of circuit, 

R = resistance of voltmeter, 

w = reading of voltmeter, 
required the resistance r across the base 
a Of to ft &,. 

Then r^R^"^ 



V 




FlO. 68. 

JHSASURBMBITT OF THB nVdlTIiA'nOir RKAIS. 

TAH CS OF Air EI<BCTItICWIJU]!f« ftYSVIDMt 

iriTH VHB JPO^TBli OH. 



The following methods have been devised by Dr. Edwin F. Northnip 
for the measurement of insulation resistance of a circuit where it is im- 
practicable to shunt ofif the current. 



1. — Voltmeter HEetiiod. 

Let A (Fig. 59) represent any wiring 
system in which Xi and X2 are the 
insulation resistances between the bus- 
bars, Bi and Bg and the earth (the 
gas or water pipes beins taken as at 
the potential o! the earthT. In Fig. 50, 
/, //. and /// are equivalent diagrams 
in which y represents the unknown 
resistance of all the lamps, motors, 
etc., across the line. 

If direct current is supplied to the 
bus-bars, a direct-ciirrent voltmeter 
should be used. If the current is 
alternating, then an alternating-cur- 
rent voltmeter will be required. The 
resistances, Xi and Xs, are determined 
by knowing g, the resistance of the 
voltmeter, and by taking three volt- 
meter readings. 

ist. Measure the voltage, which 
we will call E, across the bus-bars 
(Fig. 50) /. 

2d. Connect the voltmeter be- 
tween the bus-bar, Bi, and the earth 
and take its reading, which we will 
call Vt (Fig. 60) //. 

3d. Connect the voltmeter be- 
tween the bus-bar, B2, and the earth 
and take its reading, which we will 
call Vf (Fig. 59) ///. 

If the readings in either of the two 
latter cases are only a fraction of a 
scale division, then the insulation re- 
sistance is too high to be measured by 
this method ana we may resort to 



'j?'i f'H ^ ^ 






4!^0mmmi^ 



I B, 



fmEADSE 



Xi X, 



f READS Yl 



B., 



.'/ 



II B, 






Xi 



«MWMWWWWWIW W <WWW»»^ 



II- 



B. 



«>«READSV, 



m 



. Ca 



ci 



.'/ 



„..Ca 



Xi X, 



w 



B. 



Fio. 50. Voltmeter Method. 



MEASURING INSTTLATIOX RESISTANCE. 83 



Uieaeeood method to be described. Having taken the above three read- 
ioc*. it can be ahown that 

_ f JB - V. - V,l 
The carreat /, which leaks to the ground will be^ 

Xi -\- X2 

Per example, the insulation resistance of the wiring system of a large 
ofBee buildmg was determined by means of a Weston voltmeter, the fol- 
loving readings and resistanceB were obtained: 

a — 12,220 ohms, 
E - 113 volts, 
Vi - 1 volt, 

Kj "" 4 volts. 

X. _ 12.220 018 - 1 - 4) _ 329.940 ohm.. 
y^ _ 12.220 (113 - 1 - 4) _ ,3,,^^ ^^^ 

The above example shows that where the sum of the resistances, Xi 
and Xt, are not over one or two million ohms, the voltmeter method is 
wffidently accurate for the purpose. If one side of the line is grounded — 
tkat is« if Xz « — then from (2) E - V, + Vj - Vi, as fa - 0, and 
the metbod fails to give Xi, 

Expressions (1) and (2) above are obtained as follows: The meaning of 
the mters used are indicated in /, //, and /// (Fig. 59), Ci, Ca, etc., being 
earrents and g the resistance of the voltmeter. 

c. * 



x,+ '^' 



Xi+a 

C B 

Uj ^ ■my ' 



, or Ci - ^ 

. or Cj « -^ 

d ^ 


iff + xo 

Xi g 

ig-^x^) 
Xig 


X,+ 


gXt 


*" Xag 



Xa-i-g 

^* 'liTXt'l 

ff + JTa ' g 
Heoee, we have the two relations, 

X 4- ^^* •** ^ 

Xj + X2 -r V 

firom whieh the values for X* and X2 are obtained as given above in equa- 
tioDi (1} and (2). 

'Any uutrument, as a galvanometer, in which the deflections are pro- 
portional to the currents, may be substituted for a voltmeter. In such a 
ease, if D, dt, and d^ are deflections corresponding to the readings £, Fi, 
tod Vt, and O ia the total resistance in series with the instrument, we have 
u before: 

X «- ^ ( ^ "" ^1 " *^»^ (3) 

«d X,- g (P -/. - <<.) (4) 



84 



MEASUBBMENT8. 



If two or more electric lamps are connected in series, their resist^noeB, 
while carrying current, can be determined by means of three readings, 
as above. 

If X2 <*• 00, Vt •■ 0, and Xi — ^-^ — p ^1 which is the ordinary ex- 

V 2 
pression used in measuring a resistance with a voltmeter by reading the 

voltmeter with the resistance in series with it and again with the resLstance 
out out. 

n. — OalTaiiOVi«ter Metliod. 

This method may be used when greater accuracy is reqtured or when 
the insulation resistance to earth, of at least one side of the line, is over a 
megohm. 

Tlie wiring; system is represented in 1 of Fig. 60, and 2 of Fig. 60 gives 
equivalent circuits. 

The method consists in connecting across the bus-bars a moderately 
lugh resistance and finding on this resistance a point, p, where the poten- 
tial due to the generator vb the same as that of the earth, and then with 




Fio. 60. Galvanometer Method. 



the aid of a sensitive galvanometer and an external source of E.M.F.. meas- 
uring the resistances. Vi and r^, to earth in the following manner: A; is a key 
and S an Asrrton universal shunt. This latter may be omitted if the aouree 
of E.M.F. can be varied in a known planner. 

It is evident from Fig. 60 that a balance will be had when ? — ^ ,. the 

key, k, being in its upper position. If k is now depressed, the resistance, 
R, encountered by the current generated by the source, e, will be 



fi - J^i + 



1 



1 



1 



6 -f rj o + ri 

where gt is the resistance of the galvanometer; but in comparison with 
Ti and r2, i7i, a and 6 can be n^Iected, and « 



R - 



r,r2 



By construction, - -^ r >■ AT, a known ratio. From the last two rola- 

Tj O 

tions we deduce 

fa — - 



and 



N 
r, -/2(JV + I). 



Taking d as the deflection of the galvanometer and K as the galvano- 
meter constant, the current through the galvanometer is 

^-^.or/?--^.. 



MSASITBING INSULATIOS- BESISTANCE. 86 



K should be defined aa the reeUtanee which muBt be inserted in circuit 
with the galvanometer Cincludinc its own resistance), so that it will give, 
with one volt, a scale deflection of one scale division at the distance at 
whidi the scale is placed from the mirror during the test, usually taken 
as one meter. 

Then we will have: 

eKiN + 1) 
r, -- 



sad rt — 



Nd 
eK iN + 1) 



Tkking K ■■ 10* as an average value for an ordinary D'Arsonval gal- 
vaoometer and « >" 100, n — 2, and d — 100, we have: 

100X10»(2 + 1) ,^ , 

''» 2X100 150 megohms. 

r.- ^^^y-^^^ - 300 megohms. 

This example shows that a salvanometer of very moderate sensibility 
will measure in this wav a very nigh insulation reelstanoe. If, on the other 
hsod, the insulation is low, nmall battery power may be used or the defleo- 
ticnt of the galvanometer can be out down to V^t ihtt ii(ira> or iphn by the 
Ayrton shunt. The only difficulty likely to be experienced in applying 
the shove method is that, while ynttttinf^ the test, the relative values of r* 
sad Tf wiU keep changing, due to motors or lights being thrown on or on 
tbc line. In this event it is only possible to obtain a sort of average value 
(or the resistance to earth of eaush side of the line. 



la the United States It is unite common to specify that the entire installa- 
tios vben connected up shall have an insulation resistance from earth of at 
kiit one megohm. 

The National Code gives the following : 

The wiring of any building must test free from grounds: I.e., each main 
npply line and every branch circuit should have an insulation resistance of 
•t MMt 100,000 ohms, and the whole Installation should have an insulation 
radfttance between conductors and between all conductors and the ground 
(not including attachments, sockets, receptacles, etc.) of not less than the 
foUoving: 

Up to 5 amperes . . 4,000,000. Up to 200 amperes . . 100,000. 

Up to 10 amperes . . 2,000,000. Up to 400 amperes . . 60,000. 

Up to 25 amperes . . 800,000. Up to 800 amperes . . 26,000. 

Up to 60 amperes . . 400,600. Up to 1,000 amperes . . 12,600. 

Up to 100 amperes . . 200,000. 

All cutouts and safety devices in place in the above. 
Whsre lamp-sockets, receptacles, and electroliers, etc., are connected, 
CM>hsU of the above will be required. 
PiufsMor Jamison's rule is : 

Bceistance ttom earth = 100,000 x E-^-^- 



nimiber of lamps ' 
KsDipe'sruleis: — 

Besistanoe in megohms = i: ^-. . 

number of lamps 

A rale for use in the U. S. Navy is : 



BesisUnee = 800,000 X 



number of outlets 



S6 



MEASUBBMENTS. 



Institation of Blectrical Engineers* rule is : 

7900XE.M.F. 



Ji. 



the least li* 



number of lamps' 
Phoenix Fire, Office rule for circuits of 200 volts is that 

12.5 i|pegohni8 
number of lampH* 

Twentv-five English insurance companies have a rule that the leakage 
from a circuit shall not exceed t^hw pBrt of the total working current. 

Below is a table giving the approximate insulation allowable for circuita 
having different loads of lamps. 

For a circuit having— 



26 lamps, insulation should exceed 

GO lamps, insulation should exceed 

100 lamps, insulation should exceed 

600 lamps, insulation should exceed 

1000 lamps, insulation should exceed 



600,000 ohms. 
250,000 ohms. 
125,000 ohms. 

26,000 ohms. 

12,000 ohms. 



All insulation tests of lighting circuits should be made with the working 
current'. (See page 80, voltmeter test.) 

In the following table Uppeubom shows the importance of testing with 
the workinx voltage. 

Table 1. snows the resistance between the terminals of a slate cut out. 

Table IX. shows the resistance between two cotton-eovered wires twisted. 



] 


• 


.,. 1 


Volts. 


Mbqohms. 


Volts. 


M BO OHMS. 


6 
10 
13.6 
27.2 


68 
63 
45 

24 


5 
10 
16.9 
27.2 


281 
188 
184 
121 



M«itiiariii|r thm Innalatlon of l>jB«nao«. 

Tlio same formula as that used for measuring high resistances (see Fig. 
5o) applieH equally well to dettTmlnlng the insulation of dynamo conductors 
from tlie Iron btHly of the machine. 




Fig. 61. 



Connect, as in Fig. No. 61 » all symbols having the same meaning a« 
before. 
Let r = insulation resistance of dynamo, then 



r=7j(-,':-l). 



M2ASUBINQ INSULATION RESISTANCE. 



87 



turn MmrnmUmHawt ]KestoteBC« mf Blotors. 

Where motors are eonneeted to isolated plant oirculte irith known high 
intnlatlon, the formula used for insulation of dynamos applies ; but where 
the motors are connected to public circuits of questlonaDlo insulation it is 
aectsisry to first determine the clreuit insulation, which can be done by 
vrinf the connections shown In Fig. 66. Fig. 62 shows the conne<^tions to 
motor for determining its insolation by current from an operating circuit. 




Fig. eXL 
Here, as before, the insulation r of the total connected devices = 

.(z-i). 

If r= total resistance of circuit and motor in multiple to ground, and r, 
is the insulation of the circuit from ground, then X, the bisulation of the 

■otorwiUbe X=^^^^^. 

X«anu«Bs«Bt of th« Intoroal lt«aleta»ac« of m MmtUiry, 

Is the following figure (No. 03), let E be the cell or battery whose resistance 

is to be measured, a be a switch, and 
. r a suitable resistance. 

^k N Let V = the reading of yoltmeter 

* ■ with the key. A", open 

(this is the E.M.F. of the 
battery), and 
F^ = the reading of yoltmeter 
with key, /T, closed (this 
is the drop across the re- 
FlO. 63. sistance r), 

Then the battery resistance 

F— V 
r,=:rx — jT — - ohms. 

The same method can be used to measure the interna! resistance of 
OTosiDas. An ammeter may be connected in the r circuit, in which case 

F — V 

h ■ i — - where / is the reading in amperes. 




CmrnAmtUritj with a IHllIlvoltaietcr. 

This is a quick and conyenient method of roughly comparing the conduc- 
tMty of a sample of metal with that of a standardpiece. 

In Fig. 64, /7 is a standard bar of copper of 100% conductivity at 70° F.; 
tUs Imu- may be of convenient length for use in the clamps, but of known 
eroM section. X is the piece of metal of unknown conductivity, but of the 



88 



MEASUBEMBNTS. 



■ame croM section u the standard. J? Is a souroe of steady carrent, and if 
a storage battery in arallable It is much the better for the purpose. AT U a 
mUllToTtmeter with the contact deyice d. The distance apart of the tvo 
pointe may be anything, so long as it remains unaltered and will go between 
the clamps on eitner oi the bar*. 

Now with the current flowing through the two bars in series the fall of 
potential between two points toe same distance apart and on the same flow- 




FlG. 64. 

line will, on either bar, be in proportion to the resistance, or in InTerse pro- 
portion to the conductivity ; theref orcf by placing the points of d on the bars 
in succession, the readings of the millivoltmeter will give the ratio of the 
conductirities of the two pieces. 

For example: ^ ..,. , 

if the reading from /? =? 200 millivolts, 

and the reading from X=zW5 millivolts, 

then the percentage oonductivi^ of JT as compared with B is 

205 : 200 : : 100 : conductivity of JT, 

or — goS — ^*^*^ 



MAQNBTIC PROPERTIES OP IRON. 

BBVI8£D bt Townsknd Wolcott. 

With a giren excitation the flux ♦ or flnx-^ensit^CEof an eleetromagnet 
will d^MDiT upon the quality of the iron or steel of the core, and is usually 
iBted as compared with air. 

If a solenoid of wire be traversed with a current, a certain number of 
magnetic lines of force, JC* will be developed per square centimetre of the 
core of air. Now, if a core of iron be thrust into the coil, taking the place of 
the air, many more lines of force will flow ; and at the centre of the solenoid 
these will be equal to(j^ lines per square centimetre. 

As iron or steel varies considerably as to the number of lines per square 
centimetre (]^ which it will allow to traverse its body with a given excitation, 
its conductivity towards lines of force, which is called its permeability ^ is 
BQiBeilcaLlly represented by the ratio of the flux-density when the core is 
presoit, to the flux-density when air alone is present. This permeability 
li represented by «&. 

The permeability |t of soft wrought iron is greater than that of cast iron ; 
and that for mild or open-hearth annealed steel castings as now made for 
dynamos and motors & nearly, and in some cases quite, equal to the best 
soft wrought iron. 

The number of magnetic Unes tuat can be forced through a given cross- 
leetion of iron depends, not only on its permeability, but upon its satura- 
tion. F6r instance, if but a small number of lines are flowing through the 
Iron at a certain excitation, doubling the excitation will practically double 
the lines of force ; when the lines reach a certain number, increasing the 
excitation does not proportionally Increase the lines of force, and an excita- 
tion may be reached after which there will be little if any Increase of lines 
of foree, no matter what may be the increase of excitation. 

Iron or steel for use in magnetic circuits must be tested by sample before 
■By aoeurate calculations can be made. 



IHito for C&-3C Cnrwes. 

▲verage First Quality American Metal. 

(Sheldon.) 





w5 

^3i 


u4 


Cast Iron. 


Cast Steel. 


Wrought Iron 


^heet Metal. 


oc 


1=1 






^1 


ilomax- 
ells per 
sq. in. 


4 




5| 






Xi 


■" 


t0 


\<> 


60 


74.2 


~i3".cr 


\^^ 


be 
14.3 


wl 


10 


7.95 


20.2 


4.3 


27.7 


11.5 


83.8 


92.2 


» 


15.90 


40.4 


5.7 


36.8 


13.8 


89.0 


14.7 


94.8 


15.6 


100.7 


30 


23.^6 


60.6 


6.5 


41.9 


14.9 


06.1 


15.3 


98.6 


16.2 


104.5 


40 


31.]» 


80.8 


7.1 


45.8 


15.5 


100.0 


15.7 


101.2 


16.6 


107.1 


SO 


».75 


101.0 


7.6 


49.0 


16.0 


103.2 


16.0 


103.2 


16.9 


109.0 


SD 


47.70 


121.2 


8.0 


51.6 


16J> 


106.5 


16.3 


105.2 


17.3 


111.6 


10 


55.6.141.4 


8.4 


63.2 


16.9 


100.0 


16.5 


106.5 


17.6 


112.9 


80 


83.65i 161.6 


8.7 


56.1 


17.2 


111.0 


16.7 


107.8 


17.7 


114.1 


W 


71.60,181.8 


9.0 


58.0 


17.4 


112.2 


16.9 


109.0 


18.0 


116.1 


MM 


79.50 


202.0 


9.4 


60.6 


17.7 


114.1 


17.2 


110.9 


1S.2 


117.3 


m 


119.25 


903.0 


10.6 


68.3 


18.5 


119.2 


18.0 


116.1 


19.0 


122.7 


no 


150.0 


404.0 


U.7 


75.6 


19.2 


123.9 


18.7 


120.8 


19.6 


126.5 


»> 


198.8 


506.0 


12.4 


80.0 


19.7 


127.1 


19.2 


123.9 


20.2 


130.2 


300 


238.5 


606.0 


13.2 


85.1 


20.1 


129.6 


10.7 


127.1 


20.7 


133.6 



JC = 1.267 ampere turns per cm. = .495 ampere turns per inch. 



80 



HAGNETIU PKOPBRTtES OF 1 



ii 



^ 





1 


































i 




































. 1 












' 












































































































































5 


























































-- 














i 


































































[i 


















"•:; 


— 


j|l 


- 




■ 






\ 






1 










p 


























-- 


































> 








1 
























«i 
































si* 




' ^1 












\ 
















■fU 












\ 


















^i\\ 












!\ 
















■u 




\" 






























-F 




1 








i\ 














s 




\\ 


























- 






n\ 1 












\, 
















VMii 












\ 
















-- 


J \ 
























" 




\\ ' 






1 




\ 
















'V V 






1 
























^^■^ 
























__ 







+]^ 


=:= 


-■^4 


- 


- 






^ 


J 


L- 




r" 


^^ 






- 


T i s 






" 






- 





Fro. I. HacDatle Propartla ot Ii 



HAONKTIC TEST METHODS. 



91 



In Izrge genermtora, haytnir toothed armaturee and Ime flux densities In 
th« air-gap, the flux is earned chiefly bv the teeth. Tms results in a very 
hlfl^ tooth flux density, and a corre^pondinely reduced permeability. The 
rebted raluee of (]^, Jji£, and ft are given In the following table. These 
rallies are for average American sheet metal. 

PenH«al»IUtjr »t Hlrh Flax ]»ciBaM|ea. 





Ampere 


Ampere 


(B 


.Kilomax- 




je 


Turns per 


Turns per 


Kilo- 


wells per 


M 




cm. Length. 


Inch Length. 


gausses. 


Square in. 




200 


159 


404 


19.8 


127 


99.0 


400 


318 


806 


21.0 


136 


52.5 


eoo 


477 


1212 


21.5 


138 


35.8 


no 


637 


1616 


21.8 


140 


273 


1000 


795 


2020 


22.0 


142 


22.0 


laoo 


954 


2424 


22.3 


144 


1.8 


1400 


1113 


2828 


22.5 


145 


1.6 



OS* I»ETSRllfI!VMW« THE 9fA«lfStnC 
4fcUAI«ITIBS OF XROM AMD SVEKI.. 

The methods of determininz the magnetic value of iron or steel for elec- 
tro4iuignetic purposes are divided by Prof. S. P. Thompson into the follow- 
ing classes : MagnetometriCj Balance^ Ballistic^ and TYactUm. 

The first of these methods, now no loneer used to any extent, consists in 
eslealating the magnetisation of a core irom the deflection of a magneto- 
metw needle placed at a fixed distance. 

In the Balance class, the deflection of the magnetometer needle is bal- 
anced by known forces, or the deflection due to the difference in magnetiza- 
tion of a known bar and of a test bar is taken. 

The BaltUtic method is most frequently used for laboratory tests, and for 
sQch cases as require considerable accuracy in the results, lliere are really 
two ballistic methods, the Bina method and the lAvided-bar method. 

In either of these methods tne ballistic galvanometer is used for measur- 
iitg the currents induced in a test coil, by reversing the exciting current, or 
cutting the lines of force. 

Miac- SKethod. — The following cut shows the arrangement of instru- 
B«ntnor this test, as used by Prof. Rowland. Tlie ring is made of the 
nmple of iron which is to undergo test, and is uniformly wound with the 




BALLISTie 
GALVANOMCTBII 




•wrrcH 
9iGk 3. Connections for the Ring Method. 



cxdting eoll or circnit, and a small exploring coil is wound over the excit- 
ing coif at one point, as shown. The terminals of the latter are connected 
to the ballistic galvanometer. 



92 



MAGNETIC PBOPEBTIES OF IRON. 



The method of making a test U as follows : — 

The resistance, R, is adjusted to give the highest amotmt of ezeitlns eiu> 
rent. The reversing switch is then oommutatod several times with the sal> 
vanometer disconnected. After connecting the galvanometer Che Bwit<£ is 
suddenly reversed, and the throw of the galvanometer, due to the reversal 
of the oirection of magnetic lines, is recorded. The resistance, R, is then 
adjusted for a somewhat smaller current, which is again reversed, and the 
galvanometer throw again recorded. The test is carried on with rarious 
exciting currents of any desired magnitude. In every case the exciting cur- 
rent and the corresponding throw of the galvanometer are noted and 
recorded. 

If « = amperes flowing in the exciting coil, 
n. = number of turns of wire in exciting coil, 
/ = length in centimetres of the mean circumference of the ring, 
then the magnetizing force 



If 



3fC=^X^orl.2B7xY. 

l'^ = length of the ring in incheSt then 



If 



wC — '^wO X -p?' 

9 = the throw of the galvanometer, 
K=. constant of the galvanometer, 
R r= resistance of the test coil and circuit, 
94 = number of turns in the test coil, 
a = area of cross-section of the ring in centimetres, then 



(B= 



2 an. 



To determine K^ the constant of the galvanometer, discharge a condenser 
of known capacity, which has been charged to a known volume, through it, 

and take the reading «S then 

• 

If c = capacity of the condenser in microfarads, 

e = volts pressure to which the condenser is charged, 

then the quantity passing through the galvanometer upon discharge in 

coulomb. 1. Q= p^. 

and the galvanometer constant 

c e 



jr= 



1.000,000 0^' 



IHTid«d-Bar Bletliod. — As It is often inconvenient or impossible to 



obtain samples in the form of 
a ring, and still more incon- 
venient to wind the coils on it, 
Hopkinson devised the di- 
vided-bar method, in which 
the sample is a long rod h'^ 
diameter, inserted in closely 
fitting holes in a heavy 
wrought iron yoke, as shown 
in Fig. 3. 

In the cut the exciting colls 
are in two parts, and receive 
current from the battery and 
through the ammeter, resist- 
ance, and reversing switch, 
as shown. 



AMMrrt* 



HanoCe 




coiu {_\ oon. 

ynt^oKAiiXMOiM 

tKLLMTIO 



Fio. 3. Arrangement for Hopkinson s di- 
vided-bar method of measuring permea- 

The test bar is divided near the centre at the point indicated in 5® ^'l*: 
and a small light test coil is placed over it, and so arranged with springs as 



HAONETIC TEST HSTHODS. 



93 



Id be thitrvn dear ont of flie Toke when released by polling out the looM 
Old of the test bar by the handle Bhown. 

In opeimtion, the exciting current la adjosted by the reeletance R, the teat 
bar tnddenly pulled out by the handle, thua releasing the test coil and pro- 
doeing a throw of the galranometer. As the current is not reTorsed, the 
ladieed pressure is due to Jf only, and the equation for (Ria 



3C 



IV RK 9 
«4 



, and 



ffiX^* = l.»T^*. 



Whsre Z = the mean length of the teat rod as shown in tha out 

In uring the diyided-bar method, a correction must be made, for the rea- 
foa that the test coil is much larger than the test rod, and a number of 
Bnes of force pass through the coil that do not through the rod. This oor^ 
reetion can easily be determined by taking a reading with a wooden test 
rod in place of the metal one. 

An examination of the cut will show that the bar and yoke can also be 
' for the method of rerersals. . . 

■«tlc teiusre Hetk^d. — G. F. C. Searle iJourwd I. B. B., 

er, 1904), nas suggested another method of avoiding the use of the 

RowiuKi ring arrangement. The apparatus consists of a square, with strips 
hid oveiiapping at the edges. To obtain accurate results, the dimensions 
of the square must be large, as compared with the width of the strips. The 
Mine is true, but in a somewhat less degree, with the Rowland ring. 
Anording to A. Press, when the relative dimensions are correctly adjusted 
the ballistic galvanometer will give repeatable results, if the iron be first 
effeetivdy demagnetised by means of an alternating current gradually 
redaoed to sero, and then subjected to a series of reversals, from oO to 200 
vitk normal magnetising current, before actual readings are taken. 



( 



The following eut shows tbe method with suiBcient clearness. A heavy 
yoke of wrought iron has a small hole in one end through which the test 

rod is pushed, through the exciting coll 
shown, and against the bottom of the 
yoke, which is surfaced true and smooth, 
as is the end of the test rod. 

In operation, the exciting current is ad- 
lusted by the resistance R^ and the spring 
baUmce is then pulled until the sample or 
test rod separates from the yoke, at which 
time the pull in pounds necessary to pull 
them apart is r6ad. Then 




(B=: 1,317 X 



•Ji 



+JC- 



Where P = pull in pounds as shown on 
the balance, 

A = area of contact of the rod 
and yoke in square inches. 
JC" found as in the Uopkinson method 
preceding this. 

Following is a description of a practical adaptation of the permeam«for to 
ibop-work as used in the factory of the Westinghouse Electric and Manu- 
fietaringCo. at Pittsburgh, Pa. 



8. P. Thompson'! per- 
meameter. 



94 MAGNETIC PROPERTIES OF IRON. 



She PemteaBietcr, as med by the 1Ve«tl«fffti4»««« Klectric 

ntfCT. Co. 



Dbbiok akd Dbbcriptiok prepared by Mr. G. E. Skihiter. 

A method of meaiurine the permeability of iron and steel known as tl&e 
" Permeameter Method *^was devised by Prof. SilTanns P. Thompson, and is 
based on the law of traction as enunciated by Clerk Maxwell. According to 
this law the pnll required to break any number of lines of force yaries as tbe 
so uare of the number of lines broken. (A complete discussion of the theory 
of the permeameter, with the deriyation of the proper formula for calculatinf 
the results from the measurements will be found in the " Electro Magnet,^ 
by Prof. S. P. Thompson.) 

A permeameter which has been In use for seyeral yean in the laboratory 
of the Westinghouse Electric and Manufactiu-ing Company, and which bas 
given excellent satisfaction, Is shown in Figs. 5 and 6. The yoke, A^ 
congists of a piece of soft iron 7" x 8)" x 2}'', with a rectangular open- 
ing in the center 2^" x 4''. The sample, X, to be tested is f ' in diATn. 
eter and 71'^ lonjl; and Is introduced Into the opening through a |'^ hole in th» 

iroke, as shown m the drawing. The test sample is flnished very accurately to 
f^ in diameter, so that it makes a very close fit in the hole in the yoke. Tlia 
ower end of the opening in the yoke and the lower end of the sample are 
accurately faced so as to make a perfect joint. The upper end of the saia- 
ple is tapped to receive a i'^ screw j" long, twenty threads per inch, by 
means of which a spring balance is attached to it. The magnetizing coil. C, 
is wound on a brass spool, 5, 4/' long, with the end flanges turned up so that 
it may be fastened to the yoke by means of the screws. The axis of the coil 
coincides with the axis of the yoke and opening. The coil has flexible leads, 
which allow it to be easilv removed trom the opening for the inspection of 
the surface where contact is made between the yoke and the test sample. 

The spring balance, F^ is suspended from an angle iron fastened to uie up- 
right rack, /, which engages with the pinion, «/. The balance is suspended 
exactly over the centre of the yoke through which the sample passes, to 
avoid any side pull. A spring buffer, K, is provided, which allows perfectly 
free movement of the link holding the sample for a distance of about 4'% 
and then takes up the jar consequent upon the sudden release of the samiue. 
The frame, £, which supports the pullluff mechanism, is made of brass, and 
has feet cast at the bottom, by means of which the complete apparatus Is 
fastened to the table. Two spring balances are provided, one reading to 30 
lbs. and the other to 100 lbs. These spring balances are of special construc- 
tion, having comparatively Ions scales. (They were originally made self- 
registering ; but this was found unnecessary, as a reading could be taken 
with greater rapidity and with sufficient accuracy without the self-r^ster- 




reeling the readings. With a sample |^' in diameter, or } of a square inch 
area cross-section, the maximum pull required for cast iron is about 25 lbs., 
and for mild cast steel about 70 lbs. 

With the number of turns on the coil given above, the current required 
for obtaining a magnetizing force of JC= 300, is about 12.6 amperes. This 
is as high a value as is ever necessary in ordinary work. For furnishing the 
current a storage battery Is ordinarily used, and the variations maoe by 
means of a lamp board which has in addition a sliding resistance, so that 
variations of about .01 ampere may be obtained over the full range of cur- 
rent from 0.1 ampere to 12.5 amperes. 

The operation of the permeameter is as follows : -— 

The sample to be tested is flrst demagnetized by introducing it into the 
field of an electro-magnet with a wire core, through which an alternating 
current is passing, ana gradually removing it from the field of this electro- 
magnet. The sample is then introduced into the opening in the yoke, care 
being taken to see that it can move without friction. Measurements are 
taken with the smallest current to be used first, gradually increasing 
to the highest value desired. In no case should a reading be taken with a 
current of less value than has been reached with the sample In position, 
unless the sample is thoroughly demagnetized again before reading is taken. 
It is usually most convenient to make each successive adjustment of cur- 



THE PERU E A METER, 



nat with the umple out ot poalttoD, then Istradnoa Iha umpls uid glre It 
■ hiirnni.to ln>nr«|ierr«ct contact belwaenlheumpUsiidtbeToke. Ths 

ml^t lotrodDCt nrlon* eitott Id Ibe mauureniantg. Tbe pull it made by 
' 'If the plnkui elowlf bjr m««w of a hiuulle, E, cu-efull]' Dotlug uacL 




^ 



■ PMloB o( the Indei of the upring helmnce u It adTUicsa oTer the bci 
•M BoUng the polnl of reieue. The niMn of three or fi.ur readliig. 
?«*Ul teCen u the correoted Tslue tor pull, the correiit In the cuil renm 



} 



UAONBTIC PBOPBKTIB8 OP JBOK. 



The mugnstlilBg force JC = -737- 
Vb«reni = nnmb«ro( tonu lo Ihe mignsUiing coll = 123, 

f = lenfth of iDiuneUc eircalt Id oenllmeterm, mUib 
SobMltDtlng the kuovu ikliut In the aboie formala we hare 
3C = 13^i- 



The number of 11d« of force per iqu« 

./? + 



Where p^puU In lh«. 

^=;BreH of tlio sample In aqunre lnch«=0,306>. 
JC = ''alueof [he migDetlilng force for the slTen poll. 



THE PBRMEAMETEB. 97 

Substituting the Talue of ^ in the aboTe formnlA we hATe 

(B = 2,380 Vp + 3e 

Tliere are aerend sources of error in measurements made hj the permear 
meter which should be carefully considered, and eliminated as far as possible. 

a. The unaToidable air gap between tbe sample and the yoke where it 
paaies throosh the hole in the upper part of the yoke, together with the 
more or less Imperfect contact at the lower end of tne sample, increases the 
magnetic reluctance and introduces errors for which it is impossible to make 
due allowance. By careful manipulation, however, these can be reduced 
to a minimum, and be made practically constant. 

h. As the magnetisation becomes greater the leakage at the lower end of 
the lample increases more rapidly; and there .is considerable error at yery 
bigh values from this source, as toe leakage lines are not broken with the 
reit. 

c. Errors In the calibration and reading of the spring balance. None 
Imt the best quality of spring balance should be used, and the average of 
icveral readlnn taken with the current remaining perfectly constant for 
«Bch point on the (B'JC curve. As the square root of the pull is taken* the 
errofs due to reading the spring balance make a larger and larger percient- 
age error in (g as P approaches sero, thus preventing accurate deterxn^iu*- 
tioiu being made at the beginning of the curve. 

From the above it will he seen that the pcrmea meter is not weU adapted 
for siving the abaolute values of the ouaUty of iron and steel, but is especially 
•mtable lor comparative values, such as are noted in ordinary work, where 
* '^Tf number of samples are to be quickhr measured. A complete curve 
esn be taken and plotted in ten minutes. By suitable comparison of known 
wnples measured by more accurate methods, the permeameter readings may 
be evaluated to a sufficient degree for use in the calculations of dynamo 
ciactne machinery. 

liryedftlc's Permseameter. 

Tliis instnunent is designed to enable one to test the magnetic quality 
m^iron or steel magnet castings and forgings under commercial conditions, 
by dnOine it vrith a special drill. A testing plug is inserted in the hole 
tluM drilled and the magnetization or permeaDility is then directly mens- 



It — 


— - ^— =A. 




1" 


r. 


*l m^m ■ 




>g ' - — - 1 







Fig. 7. 

ond on an instoument attached, without any calculations, by mmply 
tiuoiniig over a reversing switch. 

Fig. 7 shows the special form of drill employed. It has four cutting 
ekes at the lower ena, which cut a cylindrical hole in the specimen. The 
<lnll ia, however, made hollow, so that a thin rod or pin of the material is 
Wt atancting in the center of the hole, as shown in Fig. 8, which shows a 
caat steel pole piece, and some small specimens of iron and steel actually 
(billed. In adaition, cutting edges are provided at the top of the drill, 
vhieh cive a conical shape to the top of the hole drilled. The hole is 
About f in. deep and ^ in. in its laig<»t diameter, while the pin is ^ in. in 
hamster. Such a hole may be drilled in any position where a bolt hole is 
afterwards to be made in the back of a pole piece, or face of a joint, or 
otherwise in projections left specially for the purpose, which may be cut 
off the Tasting or forging on delivery and sent to the test room. 



MAGNETIC PK0PEBT1E8 OF IRON. 



*^. 
/ 



Fio. a Bpsnmacis Showing Hoii 

id tha iMtiiif plug. Fig. S 

. .._li'i?uii«o" 

Ihs Bids* yield slightly and grip the f 











pus through the pin into the plug, KDd 








thence round tho muB of the mel«i to ths 








pin M»in. u .hewn in Fig. ». The pi» it 








nugnetiBd by current in > coil wound 
















is tested by use of a second or »»rch coil. 








lines of force pKasina through the search 






























lo the cb..«e m the mvetiHtion ol tb. 








CMtllE MM»»WM. 








Thse result trom Hytmti* and Eddy F 


a.O, 


Section t 


rough Plug 






uidSpeoin 




Profensor Ewing has given the name 








causes the bigaing o7 the inducfum behind th 








ma* 












heating o( the iron. 11 ineruses in direct p 
tevflnali. and acoording to Steinnisti. u the I. 


tI 


it'-lsr 


number of 


value ot Che induction in the iron cots. The h 


nl pro<lucRi has 


to be diMi- 


nted either by radialian or conduction, or by 
following torinula lor hysletesis loss in ergs 
per cycle; h-^ (B— ''. where n - a consuin 


botfi. 






*r cu 


ic centime 


t^.'^i^ 




nding upc 


n the kind 


of iron. Taking not .002 and reducing to Engl 
per cubic inch d? mstAvl Px will bo. ft - lOJ 






OS- 


V10-*. 


n which/- 



OO&B LOSS. 



99 



It is to be o L s aveJ that, in praotioe. oonsidemble variations in the mag- 
netie density take place in parts where the macnetomotive force is a con- 
stant, due to the dinerenoes in the lengths of the lines of flux. Tiiis will not 
only affeot the measured hysteresis losses, but the eddy currents as well. 
For this reason, machines of geometrically different form will not obey 
quite the same law of loeses. Considerable question has been raised 
rsffutiing the constancy of the hysteresis index. According to A. Press, 
the experiments of Mordey and Hansard with transformer iron imply that 
the hysteresis index for the range taken should be at least 2. Lancelot 
Wildkave the index as 2.7 for densities varying from (B — 200 to 0^-400, 
W. E. Sumpner states that the index varies 1.47d to 2.7, depending 
upon the range of the density, and Prof. Ewing gives the index as varying 
from 1.9 to 2 with densities (R - 200 to (B - 500. depending upon the 



Hjatsreilc Cwuitmmtm for IMirercmt Haterlala. 



Matbrial. 


Htstbretic Conbtant. 
1. 


Beet annealed transformer sheet metal . . 
Very soft iron wire 


.001 
.002 


Thin good sheet iron 


.003 


Th«»k"'Bh4«t iron . x . . , 


.0033 


Moit ordinary sheet iron 

Tnosformer cores 


.004 
.003 


Soft annealed oast steel 


.008 


^oh machine steel 


.0094 


Gutsteel 


.012 


Ckstiran 


.016 


Widened cast steel 


.025 



Hjraterciala I*o«a Factors. 



(B^ 


®— .»•• 




i»(B,^i.. 




in Gausses. 




i|- 0.002 


11-0.003 


11-0.004 


1.000 


63,100 


126 


189 


252 


2,000 


191.300 


382 


573 


765 


3.000 


365.900 


731 


1,096 


1.463 


4,000 


580.000 


1.160 


1,740 


2,320 


5,000 


828,800 


1,667 


2.486 


3,315 


6,000 


1,111,000 


2,222 


3.333 


4.444 


7.000 


1,420,000 


2.840 


4,260 


5,680 


8,000 


1.758,000 


3,516 


5,274 


7,032 


9.000 


2,122.000 


4.244 


6.366 


8,488 


10.000 


2.511,000 


5.022 


7,533 


10,044 



Eddy Currenia are the local currents in the iron core caused by the E.M.F/s 
CQccsted by moving the cores in the field, and increase as the square of the 
mmber of revolutions per second. The cure is to divide or laminate the 
on so that currents cannot flow. These cturents cause heating, and unless 
tbc eore be laminated to a c^eat degree are apt to heat the armature core so 
moefa as to char the insulation of its windings. 

Wieoer gives tables showing the losses by Hysteresis and Eddy currents 
ft one cycle per second, under different conditions. These are changed 
>Bto any number of cycles by direct proportion. The formula for eddy 
cvrentloss is: 

p» - 42 (B"2 ff* 10-", 

ia wfaidi P* — watts per cu. in., O&mm'' — maximum value of the magnetic 
deaaty per sq. in., t — thickness of plate in mils, and/ —frequency. 



HAOHETtO FBOPEKTIBS OP IRON. 



Kraterala Vacton tor I 



ATtBDIBMPATEDiT* 


I'-U 


WA™D«,PATn.AT* 


FiiEQDBNcr or One 


p; 




COHFLKTE MAONmc 


CoHPLKTE HjuiNenr 


Ctcle m Second. 


Hi 


Ctcl. rn Bko«d, 










■ .002 


ir- .003 


III 


*- .002 


^- .003 




Per 


Per 


P« 


Pbt 


Per 


Per 


P<r 


~ 




cu. ft. 








r„. ft. 


lb. 




OTlT 


1.069 


0023 


ae.ooo 


iTeT 


.0305 


22.02 


.04SS 






2.055 


!0041 


67,000 




,0313 




52 






-0045 


3.24 


.0068 


68,000 


I .3S 












0064 




































!0S06 








0137 


7i:000 


1 :5o 




21 


75 






OOM 








1 .87 




































0159 


74:000 




;0388 


2( 


41 






0111 


7.B8 




75,000 


1 .»» 


.0378 


26 


BS 


!06M 




















.0G7a 






8!73 




77I000 










.osss 




0128 


B.12 


018B 


781000 


I :is 


:0400 




78 


.0000 












1 .58 
















0204 


8o;000 




0416 




90 


.0624 




0142 


0.31 




81,000 


»:37 


0424 




S5 


oe3« 




ous 
















0048 










S3i000 




0440 






ooao 




0160 


lisi 


0240 ,■ 


84,000 


aiieo 


0448 


12 


40 


0672 




016a 


1.93 




ai.OOO 


ii.as 




»2 


98 


06S« 
























017S 


2^80 


0267 


s7;ooo 










0711 




0184 


3.22 




88,000 


13.28 


0483 


34 


87 


0724 
















(5 








01M 


4] 10 




90,000 














0202 




0303 


81,000 


4:si 


OSIO 


ta 


78 


0765 
















37 




077S 




0214 


.'i:46 




B3'wo 


^:4i 




3S 








0221 


5.S7 


0332 


B4.000. 


r5.88 


0538 


38 


















0548 


3B 


45 


















\0 


26 






0242 


7!40 


0363 


97i00O 


27! 30 














7.91 


0374 


B8:000 


27.73 


0578 


















«.1B 


0588 


12 


28 


0883 




0263 






looiooo 








85 


0808 




0270 


b:42 


0405 


105.000 


fliSO 






29 


0005 










110.000 


33.20 


0694 




80 


1041 












5.70 


0746 


53 


55 


me 




0291 


20.96 








0786 


;7 


30 


1194 




0208 


21.47 


0447 


ISoioOO 40.83 






25 


1276 



CORE LOBS. ;l{)-l 



Thm fttei^l»yftt«p Bletliod of Kjflter«ato Test. 

The samples for hysteresis tests, being generally of sheet iron, are made 
in the form of annniar disks whose inner diameters are not less than % of 
their external diameter. A number of these disks are stacked on top of 
eaeh other, and the composite ring is wound with one layer of wire form- 
ing the magnetizing coil of n, turns. This ooil is eonneotod through a re- 
Teraiog switch to an ammeter in series with an adjustable resistance, and a 
storage battery. A secondary test ooil of 94 turns is connected with a bal- 
Ustle galTanometer, as shown in Fig. 10. 

MLLirne 

QALVANOMCTCR 




STOKAQC'. 



■Revcmma 

SWITCH 

Pig. 10. 

lb make the test, adjust the resistance for the maximum exciting current. 
BererM the switch several times, the galvanometer being disconnected. 
Thsn connect the galvanometer, and reduce the current by moving the con- 
tact arm of the rheostat up one step. This rheostat must oe so constructed 
that an alteration in resistance can be made iHtkout opening the circuit even 
for an ieHstant. Note the throw in the galvanometer corresponding to the 
diange in exciting current. Follow this method by ohangin|[ resistance 
ite^-by-step until the current reaches zero. Reverse the direction, and in- 
ensse step-by-step up to a maximum and then back again to zero. Reverse 
oaee more, and increase step-by-step to the original maximum. In every 
cue note sund record the value of the exciting current i, and the corre- 
iponding throw of the galvanometer, B, Form a table having the following 
fcwidingi to its columns : — 

<, JCi •. change of (B, (R. 

TalUfW of S9xe obtained from the formula, 

3C = T^* i when I = average circumference of the test ring. 

Change of (Bis obtained by the formula, 

- la^R KB 

vhereall letters have the same significance as in the formula on page 92. 
Bemember that we started in our test with a maximum unknown value of (g. 
■ad Uiat we gradually decreased this by steps measurable by the throw of 
the galvanometer, and that we afterwards raised the (Bin an opposite direc- 
tip& tothe same maximum unknown value, and still further r^uced this to 
zero, and after commutation produced the original maximum value. Ac- 
eording to this, if due consideration be paid to the sign of the (B which is 
determined by the direction of the fralvanometer throw, the algebraic 
ram of the changes in (B should be equju to zero ; the algebraic sum of the 
int or second half of the changes in (B should be equal to twice the value 




aeuTe of JC^^<1(B' ^^® ^^^ enclosed represents the energy lost In carry> 
ing the sample through one cycle of magnetization between the maximum 
liniti -f-(Bftnd — (B- Measure this area, and express it in the same units as 
ii employed for the co-ordinate axes of the curve. This area divided by 4ir 



102 



MAGNETIC PROPERTIES OF IRON. 



gires the number of eras of work performed per circle upon one cubic c«:&ti- 
meter of the iron, the mduction being carried to the limits -f- (E<uid '— (B- 

V^e WattBi«f«r Method of HyvtemMs Testa. 

Inaemuch as the iron, a sample of which is submitted for test, is generally 
to be employed in the manufacture of alternating-current apparatus, it & 
desirable to make the test as nearly as possible under working conditions. 
If the samples be disks, as in the previous method, and these m shellacked 
on both sides before being unitea into the composite test^ing in order to 
avoid as much as possible foucault current losses, the test can be quickly 
made according to the method outlined in the following diagram : 



ALTERNAT 



Fig. II. Wattmeter Test for Hs^teretic Constant. 

Altematins: current of / cycles per second is sent through the test-nns. 
Its voltage, E, and current strength, i, are measured by the aitematins- 
current voltmeter, Y , and ammeter, A. If r be the resistance of the test- 
ring coil of »i turns, then the watts lost in hysteresis W, is equal to the 
wattmeter reaaiug fl^' — ih'. II the volume of the Iron be T cubic centl* 
meters, and the cross section of the iron ring be a square centimeters, then 
Steinmetz's hysteretic constant 




71 = 



Vf\ E\» 



i.« 



Foucault current losses are neglected in this 
formula, and the assumption is made that the 
current is sinusoidal. 

Swliisr*s Hysteresis Tester. — In this lu- 
strum en c, Fig. 12, the test sample is made up of 
about seven peces of sheet iron \*' wide and y* 
long. These are rotated between the poles of a 
permanent magnet mounted on knife edges. 

The magnet carries a pointei which moves 
over a scale. Two standards of known hyster- 
esis properties are used for reference. The de- 
flections corresponding to these samples are 
plotted as a function of their hysteresis losses, 
and a line joining the two points thus found is 
referred to in subsequent tests, this line show- 
ing the relation existing between deflection and 
hysteresis loss. The deflections are practically 
the same, with a great variation in the thick- 
ness of tne pile of test-pieces, so that no cor- 
rection has to be made for such variation. This 
instrument has the advantage of using easily 
prepared test samples. 




Feo. 12. 



Hysteresis Uteter, ITsed by General Klectric Co. 

Designed and Described by Fbaxk Holden. 

During the last few weeks of the year 1892 there was built at the works of 
the General Electric Company, in Lynn, Mass., under the writer's direction, 
an Instrument, shown in Fig. 13, by which the losses in sheet iron were 
determined by measuring the torque produced on the iron, which was 
punched in rings, when placed between tne poles of a rotating electro-mag- 
net. The rings were held by a fibre frame so as to be concentric wiUi » 



a«A«d m pointer, with 
■ bilicsl (prluK roMM 
Bd tbM nhflu Oia Tul 




top pvt o' thU iiH 
■ tbln brua STUti- 



.Dg WM put in plkG«, the 
Ina ensued wltb the tbktt, 
tlv rotated with the ringa. A 
»1tb the lower end of thsapilng 
aero of the degree acale when 
'■■ readv for na*. By tlilj ai- 
m found what diilortioQ It «M 



1 t^b *' 



le rlua, mad* 

>trioailT oppc^ 

ivolied with > masnet. 

,„ ig agalnat whioh ruhbed 

Joined through a geiialtlTa Weaton 
.. .1, II . right anglea to the 



i 



__ _ cnit being negllglWe, 

manTalDeotthecurrentia theelrcolt was proportroral to the 
Unaih the coll. Knowlngthe gonatant of (hn volimeter, ihedoflectlon wai 
tadlT ealeniated from the ipaed of the magnet, the number of lurn> fn the 

«il. Moanecti ■ -* -*■ ' "•- "'-"■ ■'* ""■"■ •" 

■dnetiun ol 2,1 



MWgaiiai 
le Bhaf t : 

ounUng. the deQectloni 
nh U« daalred Inducllo 



^e of tl 
aea, tbe 1< 



iBIerior apace of the ringi wM iK«Hglble. 
Carriwl on tbe >ha« below the msgnet wa« a pnllay aro 

8* wiull be found by obaerTlng that 
to be produced on tbe Toltmeten 
I In the rings, were flnt calculati 



104 HAGNETIC PROPBKTIES OF IBOIf. 

rvTolntloaa par mlnnte vu genarallj udoptod u the ipseil In thb aaso. 
Ttis molor being run at the dHlrsd gpeed, Cbe magnetliliiE onrrant iru mA- 

Ctted until the caloulHteddaH action vu produced^ou tbe vDltmaUir. KMp- 
t tbc magnaticlng aurreutoonttADt, tbe^peed waa changed aucoaaaWalj In 
Talua to certain Tsluea, and the corrv«p>indlng cllglortlans of tba Bpriac 
ti»c»aarT to balance tbe affect of the magnet noted. When tbla prooeaa 
waa cairM out at dlffsrenl inductinn values, and tbe ergi eipundxd par 

Sroduced, as ibowaln Fin. 1* and IG. It waa found tbat tbe ilope of itao 
nee decreaaed veij rapldlf wltb tbe deoreaee In tbiokneea of (he Irun aheet 
uaed ao u to Indicate tbat had it been cbln euougb ibe ilope would tuiT« 
been lero between 100 aod SOO revalutlons per mlnule, which wag abuat ths 
higbeat speed penniaalble. From tbii It would eeBni ibat. In these taeta, th« 
total loBB per c^cle bad two componenla ; one remaining canatant, due to 
hyatereala, and [be other larylng ae tbe gpeed it tbe magnate, due to anr- 

Fla. ISglrea obeervatloni oleddjcuneut loMand thlckneea of iron aheet 
on this aaamnpUon. Tbe line drawn la a Mrabola, ao tbat II would appeu- 



ranee of obaer 
•aid thaatieet 



Fig. 11 glTea Unea troi 



taken lower 



the Unea , ,„ ^ _ — „, 

read with tbe tacbometer arallable for tbli partkuliLr teal. Plotting the 
hntereala ae a function of the lndu(;(bm. In (his caae tbe polnta are all qolt* 
otoaa to a curve wbuae equation la, Krgn = A constant X (Uenalty peraquarB 
caatlmeter)'", three points In the Utter cnlculHted curre beliig ahown by 

tblck. and ibowa a greater eddy current loss. Tbe equation for the byitere- 
sle curve tor tbla aaniple la, Hrgn ^ A constant x (Density per square oenti- 
melera)'-', some points In the laller curve being shown bycrosees.aa before. 

the Induction In Fig. IT. The cunw dr:iB n are paraliolas; ahowJng that In 

Induction, altboQgb there were often greater varlatli>ns from tbat law than 
these two samples abow. The average exponent tor tbe hyatereala cnrrea 
was a little over 1.5, although It varied Irom t.4 to I.T. Sings tested In tbla 

ftep-by-atap method. There were dtscrepanclee of n« much as 4 per cent be- 
tween the two resalle, but an average it ten teeCB ahowed the balllstlc^il- 
Tanometer method gave results 2.6 per cent lower than the other. Tbia 
difference la eaailv attributable to eiperlraental errors. 

It being noticed that for a given indactlon In the rings, the masnetlalag 
eurrenta for dlffeient aamplea did Dot vat; much, it waa planned shortly 



lEM eompIaUng tb« mboie tppuatu* t. 

■hiebwoDktnM«leetTO-iiiagneU ot ■nchhlghTelucti^.- .--.. 

ofUieringewoiildb«negllgtbl*,»iiiili»lo«on 

._„_, be d«nii3eD( only on Uie cuirent fly maliln • 

^^^^BBM^DBn^ Uis electio-inuDeta ot soluble Iron uin ot 

I Ifa^r 1 rtK,nt«i»-tWrftli8croM-«Kilono[ tberlLji 

*^^^^S»S^^** uHHl. the Iron muj be no LlgbU wtumled 

ts^_^ UMt tbs Induction *iLl ™m^Qqiiile coi..liiiit 

Pio. H. Hodlfled Hy>l«r- under eoiiHlderable Tarlnlion In "^ ";»8""- 

«i, Meier. !^J«„™"£, co "p.tToS! "^ r«J"e^z?nl 

oorronti, imd the f Inra can be at ■boat their 

mulBiiiin penneBbllltT irhen tboi msgnatlied. Such an laatruroeht 1* 

item in Ft la ill luioriglntil eiperlmental Iorni,»^th the rinm In potlHon 

nd) tor ^1. A oiotRaed form i. shown In Kg. IB. Tie ring, are 

Iwn. .llo«ed to rotate In opposition to Ibe action ot H^priag and tarry ft 

pranter oxer a scale, so that II In qnlte direct reading. Twenty^vo oompar- 



i 



koM of this [Ditrainent irlth the original one gare reanlti that >cre*d 
■tihlD a per cent In all caeca, and more than half were within 2 per cent of 
•fnwnent. Permanent mBgnela had been preTlouilj tried, but the attempt 
Koud to (how (bat tho Inatrnment would not, In that caae, compare sam- 
plci ol Iron vldelT different In character ; and tbe writer not being able to 



Fio. IS. 
the taj attention to tbe matter, no further lnTe«llgatlonj la that direction 

Ttic inatrumeni tint deacribed has been In use contlDuonily alnco itii com- 
(latlon at the worke of the Oenatal Electric Company, In Schenectady. 



106 



MAGNETIC PROPERTIES OF IRON". 



MI»I»ir CVlftltBllT FAOTORA 

coRB DKirftnniBS a]Vi» for tarkovs 

IiARXlTATIOirS. 

(Wie&er.) . 



o5«o 






10,000 
16,000 
20,000 
26,000 
30,000 
31,000 
32,000 
33,000 
34,000 
36,000 
36,000 
37,000 
38,000 
39,000 
40,000 
41,000 
42,000 
43,000 
44,000 
46,000 
46,000 
47,000 
48,000 
49,000 
60,000 
51,000 
62,000 
53,000 
64,000 
65,000 
50,000 
57,000 
68,000 
59,000 
60,000 
61,000 
62,000 
63,000 
64,000 
66,000 



Watts dmsipatkd 

PKB CUBIC FOOT OF 
IBON AT A FRB- 
QUEKCY OF 1 CYCLE 
FEB BBCOKD. 



Thickness of laminatioii,< 



.010" 


.020" 


.040" 


.0007 


.003 


.012 


.0016 


.007 


.026 


.0020 


.012 


.046 


.OOtf 


.018 


.072 


.0066 


.026 


.104 


.0070 


.028 


.111 


.0074 


.090 


.118 


.0079 


.032 


.126 


.OOM 


.034 


.134 


.0060 


.036 


.142 


.0094 


joas 


.150 


.0009 


.040 


.158 


.0104 


.042 


.167 


.0110 


.044 


.176 


.0116 


.046 


.185 


.0122 


.049 


.194 


.0128 


.061 


.204 


.0134 


.064 


.214 


.0140 


.056 


.224 


.0146 


.000 


.234 


.0153 


.061 


.246 


.0160 


.064 


.266 


.0167 


.067 


.267 


.0174 


.070 


.278 


.0181 


.072 


.289 


.0188 


.075 


.300 


.0196 


.078 


.312 


.0202 


.061 


.324 


.0210 


.084 


.337 


.0218 


.087 


.349 


.0226 


.001 


.362 


.0234 


.004 


.375 


.0242 


.007 


.389 


.0261 


.101 


.403 


.0260 


.104 


.416 


.0269 


.108 


.430 


.0278 


.111 


.444 


.0287 


.116 


.458 


.0296 


.118 


.473 


.0306 


.122 


.486 



.060" 



.046 
.104 
.185 
.288 
.416 
.444 
.472 
JS03 
J69i 
.567 
.600 
.633 
.667 
.703 
.740 
.777 
.816 
.855 
.896 
.987 
.979 
1.022 
1.066 
1.110 
1.066 
1.200 

l.ifflo 

1.297 
1.346 
1.397 
1.446 
1.500 
1.666 
1.610 
1.666 
1.720 
1.776 
1.833 
1.891 
1.961 






66,000 
67,000 
68,000 
69,000 
70,000 
71,000 
72,000 
73,000 
74,000 
75,000 
76,000 
77,000 
78,000 
79,000 
80,000 
81,000 
82,000 
83,000 
84,000 
86,000 
86,000 
87,000 
88,000 
89,000 
90,000 
91,000 
92,000 
93,000 
94,000 
96,000 
96,000 
97,000 
98,000 
99,000 
100,000 
106,000 
110,000 
116,000 
120,000 
126,000 



Watts dissipatbd 
per cubic foot of 
tbov at a krb> 
quevcy of 1 cyci<b 
pb& second. 



Thickness of lamination, S 



.010" 



.0316 
.0325 
.0336 
.0345 
.0366 
.0366 
.0375 
.9386 
.0396 
.0407 
.0418 
.0429 
.0440 
.0451 
.0462 
.0474 
.0486 
.0498 
.0510 
.0623 
.0535 
.0648 
.0660 
.0673 
.0686 
.0699 
.0612 
.0625 
.0638 
.0661 
.0666 
.0679 
.0693 
.0707 
.0722 
.0797 
.0675 
.0056 
.1040 
.1128 



.020" 


.040" 


.126 


.503 


.130 


.519 


.134 


.634 


.138 


£60 


.142 


.566 


.146 


£82 


.150 


JBOB 


.154 


.616 


.158 


.633 


.163 


.660 


.167 


.668 


.171 


.686 


.176 


.708 


.180 


.721 


.186 


.740 


.190 


.758 


.194 


.777 


.199 


.796 


.204 


.815 


.209 


.836 


.214 


.866 


.219 


.876 


.224 


.896 


.229 


.916 


.234 


.937 


.240 


.968 


.245 


.979 


.250 


1.000 


.266 


1.021 


.261 


1.043 


.266 


1.064 


272 


1.066 


.277 


1.109 


.283 


1.132 


.289 


1.156 


.319 


1.274 


.360 


1.396 


.382 


1.528 


.416 


1.664 


.451 


1.806 



.080" 



2.013 

2.076 

2.187 

2.200 

2.285 

2.380 

2.386 

2.483 

2JB» 

2.800 

2.870 

2.740 

2.810 

2.888 

2.968 

3.038 

3.108 

3.184 

8.280 

8.840 

3.420 

3JS00 

3JM0 

3.682 

3.746 

3.880 

3.915 

4.000 

4.085 

4.170 

4.257 

4.345 

4.436 

4.528 

4.622 

5.006 

6.598 

6.113 

6.6S5 

7.28S 



ELECTROMAGNETS. 

PIftOPfiJRTlES Ol*. 

RXYISJCD BY TOWVBKSD WOLCOTT AJXD PbOF. SAMURL SHKLDOX. 

Reaidtuil MctoneHtm is the ma^etieation remaining in a piece of mag- 
netic material after the magnetiniu; force is discontinued. 

RetenHveness is that property oi magnetiaable materials which is mnns 
ured by the residual magnetism. 

Coercive Force is the magnetising force neoessary to remove all reeidual 
magnetism. 

PermaTient maoneHam is residual magnetism in a material of creat coer- 
cive force, as hard steel, which has little retentiveness; while soft iron has 
great retentiveness but little coercive force. 

The following paragraphs are condensed from 8. P. Thompson's "The 
Electromagnet : '* 

Hagm^to-MottT* force. — The magneto-motive force, or magnetl*- 
liig power of an electro-magnet Ia proportional to the number of turns of 
wire and the amperes of current flowing through them ; that is, one ampere 
flowing through ten coils or turns will produce the samema^iMtoHBiotive/wvf 
aa ten amperes flowing through one coil or turn. 

If n == ja umber of turns In the coll, 
/= amperes of current flowing, 

1.267 = ^ (to reduce to C. G. S. units). 

Magneto-motive force = 1.257 x n/= ^. 

Xtki/^nalitj of REacnotlc Force. — Intensity of magnetic foroe in aa 
electro-magnet varies In different parts of the magnet, being strongest in 
the middle of the coil, and weaker toward the ends. In a long electro-mag- 
net, say a length 100 times the diameter, the intensity of magnetic force wiu 
be found nearly uuiform along the axis, falling off rapidly close to the ends. 

In a long magnet, such as described above, and in an annular ring wound 
evenlv over ite full length, the value of the magnetic foroe, JC* >* deter- 
mined by the following expression :— 

3C== 1-257 —r- , in which {= centimeters. 

If the length la given in inches, then 

5C.= .496-^ , in which l,,^ Inches. 

If intensity of the magnetic force is to be expressed in lines, per sq. ln<^ 

JC/,= 3.198 x^. 

Valve of JC ^^ <^« centre of a Mncle-tiini of Coaductor.— 

In a single ring or turn of wire of radius r, carrying / amperes of current 

3C= I X ^= .6284 X ^ 

-Force on Conductor (cnrrjl nir cnrrent) 
In n mnynetlc Field. — A conductor carrying 
current in a magnetic field \» repelled from the 
fleld Dv a certain mechanical force acting at right 
angles Doth to the conductor itself and to the lines 
of force in the field ; see Fig. 1. 

The magnitude of this repelling force is deter- 
mined as follows, assuming the field to be uniform : 

ft 

JP =r magnetizing force, or intensity of the fleld. 
I = length of conductor across the field in cm. 
I,. = ditto in inches. 

/ =r amperes of current flowing in the conductor. 
F r= repelling force. 

:=3^i/. Jf in dynes =?^"'^'/ 
10 ^ 25.4 




F in dynes = "^^^ • F in dynes = 5^^;; j' -' . ^ in grains = 



Fio.l. Action of Mag- 
netic Field, on Ckm- 
duotor carrying cur- 
rent. 

UV// » // / 

16146 ■ 



108 



PBOPEBTIBS OF ELECTROMAGNETS. 109 



'mriL 4Lmm9 lajr GoBdvcior (e^rwyiw^p Cnnreat) te aioviaf 

acroas m Magmetlc field. 



If the conductor described In the preceding paragraph be mored acroM 
the Held of force, the iiik>rk done will oe determined as lollows : in addition 
to tbe symbols there used, let b = breadth of field in and acroM which the 
ecmdnetor is moTed ; «o ^ work done in ergs. 

5/ =: area of field, 

If=blx^ = number of lines of force cut, 



of Comlvctor (oarrTin^ carrent) »ro«ad a V/Lmffn^t 

Pole. 

If a eondnctor (carrying current) be so arranged that it can rotate about 
Ob pole of a mamet, the force producing the rotation, called torgtu, will be 
aeterniined as f^lows : The whole number of lines of force rad i a t i n g firom 
the pole will be 4 v times the pole strength m. 

DlTidlng by the angle 2v, the torque^ T, is 

T Z^ "Tn" —- '2 flu, 

Xverif eleetrie efrcuii tends to place itself so as to embrace the masckmim 



TWo eieetric oonduciors caarryina cwrraUs tend to place themselves in poeitkm 

"'' that their mutual flux may oe mctxvmum ; otherwise stated : if two cur- 
I ran parallel and in the same direction, each produces a field of its 
own, and each conductor tends to more across the other's field. 

In two coils or conductors lying parallel to each other, as in a tangent gal- 
ranometer, the mutual force vanes directly in proportion to the product of 
their req>ectire n/,and inversely as the axial distance they are apart. 

PrlBCi|»le or «!■• IHofvetlc Circuit. —The resistance that a mag- 
netie circuit offers to the nassage or flow of magneiie lines of force or fiux^ 
has been given the name of reluctance^ symbol (^, and Is analogous to resist- 
mneej to the flow of electric current in a conductor. 

The magnetic Jiux or lines of force are treated as current flowing in the 
flsasnetie oirenit, and denoted by the symbol ^. 

The above two factors, together with thomagneto-motive force described in 
the eurly part of this chapter, bear much the same relation to each other 



do resistance, current, and E.M.F. of electric circuits, and are expressed 
follows: — 

Maimetitt flux - Magneto-motive force 
" reluctance 

<F=^'= 1-287 n/. 

._ 1.257 n/ 

1.257 



110 ELECTKOMAGNETS. 

If dloMiudoiis are in inoh«s, and A\Bin Bqnare inches, Umb 

and ^ = (B" A", 

TMe Itaw of Tmctloa. — The formula for the pnll or lifting-power 
of an electromagnet when the poles are in actual contaot with the arm*> 
tare or keeper is as follows : 

Pull (in dynes) = ^ 

8 IT 

Pull (in grammes) = ^^^^^ • 
PuU (in pounds) =^j^P^. 
In inch measure: Pull (In pounds) = -^ «^ooo ' 

Traction. 

This proportionality to the square of the induction aooounts for some 
anomalous peculiarities in the way that the keeper of a magnet holds fast 
to the poles. If the pole faces be perfectly true and flat and the face of 
the keeper the same, the keeper U actually held with less force than wheo the 
I>ole faces are very slightly convex. Or, aflnin, if the keeper be slid to one 
side until only its sharp ease and that of the poles are in contact, it will be 
found to adhere more firmly than when placed squarely and centrally on 
the poles. In general, a magnet holds titter to a slightly uneven surfaoe 
than to one which perfectly fits the poles. The reason is that, when the 
area of contact is decreased, the intensity kA the induction throuf^ the 
remaining contact is increased by the crowding together of the hues of 
induction; and, as the traction is proportional to the product oi the area 
and the square of the intensity of the induction, so long as there is sufficient 
crowding of the lines so that the square of their intensity increases more 
than the area is diminished, the traction is inoresised by inducing the area 
of contact. ^^ 

The amount of the traction is usually determined by the formula, T =: ^^< 

in which T is the traction per square centimeter expressed in dsmes: to 
express the taaction in grammes, this ficnire is of course divided by 981, or 
for pounds avoirdupois per square inch it should be divided by 60()O0. 
This formula is correct tor the force required to separate the halves of a 
straight bar mafcnet out in the middle, if the winding be also in halves and 
these halves separate at the same time as their respective halves of the 
oore and if, further, the winding fit the core closely. It is also oorreet for 
the separating force when the magnetism is residual; as in the case of a pet^ 
manent magnet. In other oases, for example, where an ordinary keeper is 
pulled away from a magnet, the formula is not strictly accurate on account 
of the keeper being attracteid partiv by the core of the magnet and partly 
by the current in the winding directly. However, the attraction exerted by 
the coil is usually small as compared to that exerted by the core; and the 
formula is not very much in error. 

The attraction between the two parts of the iron is always 2 w^ dynes 
per square centimeter, ^ being the intensity of magnetisation, that is the 
number of units of free magnetism per square centimeter. But (gr=4 v^ 
+ 5C 80 when J(^ = 0, that is when there is no magnetizing force, 2 «(5a 

/o« 
=: ^ , which is evidently correct, as there is no attraction except between 

the two parts of the iron. When JC '" "^^ equal to zero, that is, when the 
magnetism is not residual, there is a force between the coil and the ]>art of 
the iron that is move<l away from the coil equal to J(^, 3 fis^es per square 
centimeter, so that the whole force of separation is 2 ir^* + 3C 3* "^lien 
there is a coil on each part of the magnet and both parts of the magnet 



PBOFBBTIES OF ELEGTKOMAOXET8. 



Ill 



the 



the 
the 
the 
but. 



tkmbet 



both ooils are just alike, there are two of these 5C0 forces, because 

eofl attracts the other part of the iron; but as in this case ^ represents 

intensity of the magnetising force €i the whole coil each half now 

the other part of the iron with a force of ^—^ and both forces 

2 T^l 

equal JC5- The two eoils attract each other with a force of^ 
square oentimeter. so the whole force is2ir3*+3C3+ ^^. which 

be written^ (l<Jw»5» +8»5C3 + 5e«)-^(4»3+3e)»-^ 

square centimeter, so in this case also the traction is proportional to 
square of the intensity of the induction. If the eoils be loose upoo 
eoras so that their areas are sensibly greater than those qt the cores. 
whole force of separation is fp-eater than that aiven by the equation; 
in praetieal cases, the error is usually small. ' In all eases, the attrao- 
''-* the iron parts is 2 «- (P per square oentimeter. 



Tr«ctl«M •f Slectr* Mm^pmmtB* 



A 


(ft'/ 


Dynes 


Grammes 


KllogB 


Pounds 


Lines per 


lines per 


per 


per 


per 


per 
sq. inch. 


sq. em. 


sq. inch. 


sq. cm. 


sq. cm. 


sq. cm. 


1,1100 


6,400 


30,790 « 


. 40JS6 


.04066 


jm 


2,000 


12,900 


169,200 


162.3 


.1623 


2.306 


9,000 


19,360 


368,100 


366.1 


.3661 


6.190 


4,000 


2B,aoo 


636,600 


648.9 


.6489 


9.228 


ffiiOOO 


32,260 


994,700 


1,014 


1.014 


14.39 


iJOOO 


38,700 


1,432.000 


1,460 


1.460 


20.75 


7J0OO 


46,160 


1,960,000 


1,987 


1.067 


28.96 


MOO 


51,000 


2,647,000 


2,696 


2.606 


36.96 


9A» 


68,060 


3,223,000 


3,286 


3.286 


46.72 


10,000 


64,600 


8,979,000 


4,066 


4.066 


67.68 


11JU» 


70,160 


4,816,000 


4,907 


4.907 


69.77 


13,000 


77,400 


6,730,000 


5,841 


6.841 


83.07 


13JD0O 


83,860 


6,726,000 


6,866 


6.866 


97.47 


14,000 


90,300 


7,800,000 


7,660 


7.660 


113.1 


15,000 


96,760 


8,963,000 


9,1'^ 


9.124 


129.7 


lf,/00O 


UttJUO 


10,170,000 


10,300 


10.390 


147.7 


17/100 


100,660 


11,600,000 


11,720 


11.720 


166.6 


18,000 


116,100 


12,890,000 


13,140 


13.140 


186.8 


»JBO0 


122,660 


14,360,000 


14,630 


14.630 


208.1 


»,000 


129,000 


16,920.000 


16,230 


16.280 


230.8 



■xcitii 



»srcr mrn^ TvACtlOM. — If we can assume that there is 



no magnetic leakage, the exciting power may be calculated from the follow- 
iqg expression; AUdtaneDSions being in inches, and th^puU in pounds: 

,»7=ffi^'x.3132. 
^ ~i"X.3132' 



also,(B^'=8494y^ 



PulT 



Area" 

fll/=2061 X — X y • 
If dimensions are in metric measure, 

r=3961 -^ 



Area" 



«/: 



Pull in kilos 
ji Y Area In sq. cms. ' 



*» T Area in sq. ins« 



oi=««v's: 



Pull in kilos. 



Area sq. cm. 



112 



ELBGTR0MAQNET8. 



^fmmilf « OV EJLECTl»OMA«mET0. 



The method uaed by Cecil P. Poole for predetermining magnet windinn 
is as follows: Temporary test ooils, of wire much larger than wiU probalMy 
be required in the permanent coils, are wound to occupy the space th&t 
it is estimated the permanent coil will occupy. Current ia passed throueb 
the temporary coils in series with a water rheostat or finely graduated 
reaiatance, by means of which the excitation may be oloeely adjusted, 
llie exciting current is adjusted until the desired magnet pertormanoe is 
obtained; the current producing this e£Fect is represented by /«. Tlie 
current is then increased or decreased as may be required imtil the resist' 
anceper foot of the winding corresponds with the resistance per foot given, 
by Table I herewith, after five hours. The current required to produoe 
this result is indicated bj^ Ih, 

The size of wire required to produce a given nutnber of ampere-turns 
under given conditions of mean length and voltage is 



€P 



KAtLm 



in which eP equals circular mils of the wire to be used, JT is a ooeflScieiit de- 

§ ending upon the specific resistance of the wire, A t equals the ampere-tums 
esiredV-^ equals the mean length per turn of wire in inches, ana V equmls 
the volts at the terminals of the coil. With the best commercial graoe of 
magnet wire, K becomes unity at a temperature of about 140" Fanr., since 
the resistance per mil-foot of the wire at that temperature is 12 ohms. 
The resistances of wires given by Table I are based on this temperature. 
Table II has been calculated from the foregoing formula for this temper- 
ature. 

From the first test made with the temporary winding the desired ampere- 
turns are obtained, and from Table II the sise of wire required to give the 
nearest number of ampere-tums per volt corresponding to this test and the 
proposed working voltage may be obtained. 



Table I. — 




e« irire at \4M» Tent] 
•ft. 



Wire No. 


Resistance per Foot. 


Wire No. 


Resistance p^* Foot 


4 
5 
6 


0.0002875 
0.0003625 
0.0004571 


19 
20 
21 


0.009316 

0.01176 

0.014814 


7 
8 
9 


0.00057662 

0.0007268 

0.0009168 


22 
23 
24 


0.018601 
0.023575 
0.0297 


10 
11 
12 


0.001156 
0.0014575 > 
0.001838 


25 
26 
27 


0.0375 

0.04725 

0.05956 


13 
14 
15 


0.0023175 

0.002922 

0.003684 


28 
29 
30 


0.0751 
0.0947 
0.1194 


16 
17 
18 


0.004646 

0.00586 

0.007389 


31 
32 
33 


0.1506 
0.1899 
0.2395 



WINDING OF ELECTBOHAGNETS. 113 



Thm number of turns of wire in the test coil will, of oourae, be known, 
mod the product of thiB number and the current, /•. u the required exciting 
force in uiq>ere>tums. The mean length per turn of wire in the perma- 
nent minding will be the same as that in the teet winding, subject to minor 
oonections that may prove necessary in rounding out the final results. 
Tentatively, at least, the mean leqgth, L», will be equal to 

in wfaidk Gt is the i^rih of the test coil and g the girth of the bobbin of form 
in whi^ it was wound. Having the ampere-tums required, the mean 
leoKtli per turn of wire and the voltage that will be applied to the terminals 
of tne coil (or each coil, iJf there are more than one), the sise of wire that 
inuat be used in tiM permanent winding is obtainable by the application 
fd TaUe II. It may nappen that none of the mean length values in the 
table will be found to correspond with that of the test winding; in that 
event, the nearest talt>ie value may be adopted and the mean length per 
turn of the permanent winding made to conform to this. In many cases 
it will be found that both the excitation per volt and the mean length per 
torn of the test winding will differ from all values in the table; in such a 
ease, the nearest meanlength value in the table should be adopted which 
gives the nearest excitation per volt in exeett of the desired value. 

Hm table is worked out on the assumption that any two wires drawn to 
B. A 8. gauge and differing in sise by ten gauge numbers will have cross- 
sectiooa] areas differing in the ratio of 1 to 10.163 or 10.103 to 1, according 
to which wire is considered first. 

As stated in the note at the foot of the table, the amp^-e-tums per volt 
in eolmnn a apply to the wire sises in line A across the top of the table: 
tikc ampere-turns per volt in column b apply to the wire sixes in line B, ana 
those in column e, to the wires in line C. Thus, if a coil wound with No. 
S wire has a mean length of 45.11 inches per turn, its exciting force will 
be 366 ampere-turns for each volt at its terminals; a coil of the same mean 
lenpith 'but wound with No. 18 wire will have 36 ampere-turns per volt. 
whDe a ooil of No. 28 wire with the same mean length pa- turn will yiela 
oniy 3.54 ampere-turns per volt of applied E.M.F. The table is calculated 
OB the basis of the wire sises in line B and the ampere-turns per volt in 
eDhmm 6, henoe the latter values are not numbers from which dedmals 
have been dropped, but are exact. 

If the winding is to operate at constant potential, as most magnet wind- 
ings do, the watts dissipated will be exactly proportional to the current 
ps Sling, and this will be invers^y proportional to the length of the ooil par- 
alel with the magnet core if the s:irth and temperature remain constant. 
The temperature will be imchangeoTof course, the value A, of the current 
seesssary to produce the working temperature having been ascertained by 
trial, as previously described. If the girth of the permanent winding 
cannot be made identical with that of the test winding, the correction in 
dimemions will be simple. First, the proper length on the hypothesis of 
anebanfed girth must be detemuned. As the temperature of the coil is 
a function of the heat dissipated per unit of effective radiating surface, 
and the radiating surface is approximately proportional to the length of 
the ooil parallel with the core (assuming the girth fixed), the heat disn- 
pated per unit of surface will be approximateiv proportional inversely to 
the square of the ooil length. Therefore, if the girth of the permanent 
winding were identical with that of the test windingi the proper length 
of the permanent coil would be given Ky *'' equation. 

IrtX /^-L. (1) 

in which L* is the length of the test ooil and Le the eaiculated length of the 
permanent eoil on the basis of unchanged ^rth. Table III (divided into 
ibttr sections. Ilia, Illb, Ille and Hid,) ^ves the corrected ooil length, 
Lc, corresponding to a considerable practical range of test coil lengths, 
L^ and ratios oi /• to /*• If no correction in the mean length per turn 



114 



BUDOTBOHAaifETS. 




t 
I 



I 

1 

e 

B 

H 

k 

I 

i! 

m 

t 

fl 

I 

fl 
e 
6 

a 

R 

I 

• 

H 
H 

9 
I 



CO 



!^ 



»o 



»0 



•* 

-^ 



«5 



CO 
CO 



CI 






04 






^$4<-i^C4 cQiooo>-«o aboot^M tviHioOtO 

uQ^coci^ oa»aooor«^ oio-^'^co cio)<-«i-^c> 

tOiOOOOIb- 
^CO WCw06 

V^Hoo'toeo 

coo «D 

cieooooo 
2<r^eooii 

^iovhoco <»t««i-4(o <S c!iooo» OtoStOO 

^Jtrdsiff »-<o6Maeod ofi^'d«5co -^0050^53 

oaoSoooo ootN.r«t«h- oootoio io9-9^-« 

^a»^eo<D cotoScI «-4t^Sr»S ioiot<>'^oo 

Ooih^Mh^ C09iOC9O> fOQiOr-^t* '^'HOQ^OCO 

6lC4^^0 OS0»0»00 00Q0t«r^«O «DCO>OiO<0 

o»^rH(Dt» cieococoeo uSi^oo^h- 'ifuSooooo 

C4»OQQi-4iQ Q>OQ(00« 00*-*i90!0 ^l<*^Or* 

cDuS^^m eoc(c9«-4*-4 oooSSoo oot^-ror^e 

coooh*co-i cioS^hSo °^.^^ . <ot^eocsik5 

tOQOQOad^ ^^•c^«P^ tdood'^qo c^^codtn 

OOOOKt^ <OiOiO^'^ €00404^0 OOtOOOOO 



CI 


s^ 


CI 

CO 


vMiovHoSt^ «SSb>SrH <<iioSSdn Se^icSco 

ssass sssisa ssssss sssss 

• 


t-4 


CI 


CO 


40.5 

38.67 

36.82 

35.22 

33.75 

32.4 

31.15 

30. 

28.95 

27.93 

27. 

25.31 

23.82 

22.5 

21.31 

20.26 
19.28 
18.41 
17.61 
16.87 





s 


s 


rH«5<^9hS ooco^iocs ookdcooo ScommS 

iiii9 ii^ii isiii iiiii 


a> 




s 


iiiii iitiii ii^ni iiiii 


» 


00 


s 


sf:s:s^ s^sss ssijiiiii iiiis 



u 


t^r<*«oo« <0(p<piou2 ioio:i«-<f'« ^cocococ« 
aoi-fcico '«*u5«t>.o6 o5»Meo»ii> di-<coioi^ 

^cJcicici cicicic4C4 cicoeocoeo co**^^-"* 


iO 


Sc^g^S^^ ^^^^^ UU^^^ ?^999 



O^deo"* 

RC4CICICI 



'h' '4; ^ ' 
C4C4C4< 



COCOCOCOCO ^^"T^^ 



^■B 



=1 



WINDINO OF ELBCTR0MA6NBTS. 



116 



s^^s^ ^^^,^,^ ss^ss ^^,^^^, 

oc»aor»r>- <o«Dioio>o lo^^eooo cocqoc^m* 

aeor^QO^ SotS^to ^QOnSS ^ot«>oM 

e««^c>oie» aooot«r*o oious^^ ^^coeoeo 

o<^eo94'H ooo»a»ao oot«^<D<OiO loiO'^^V 

^^^^<> ^^,^^^, ^^^^,co ^^^^^. 

QXr«>iO'« e09«C«^O OOkOOt^r* ««0«C>iOiQ 

h--«7ao^ ^^rHeo>3 SBt^b^Okci lOo>o^^* 

gn-^okoo t^cDio^eo ct^ooob Qooot-b^td 

9ioo3m veo^oo e>4t«>io^Q0 oo^uSoio 

nAfx-^eo •-•do»«t« <o^eQC4«H ddo»o>od 

eOfiCldOt C*CiiM»Hw^ (Ir-liHt-lr^ i-Hi-H 

c«<-«49l cQOot*»o ^«Dot-co ooooeot* 

Qr«^^9 t-w)^c^^ OQOt^io^ eoc«e4i-td 

#eoeoeQci c)clc^C4C« e5,-«^^iFS ^^^^^ 

SSSi«Cft 9Smi»<-4 So^udSo^ Sl^*<^^S 

i-i9»dd ^oioQDt^ uam^doo r»«io^oo 

to^'^mn eoeocoeic^ eIe«c«t-«.-« p^ri^»-ii-t 

^C««C«4eO CO<-lMOQQ |x.*H^iA«9 •-•lQ<Da'« 

-»c«5i--»<5 ^t^eo^N udOi-ioci b»w»-«o«-< 

ss;ss$ ma ui^^^ ^^ii^ 

^KiQOh- O^CimCO r^MMOcO €Qr««0f-H«-4 

^o7*>40 »«eoeo«c< ococnoco nce^ooo 

ei^gDeoco ^"-"OQiQeo .-it-^^a* b-iQ^cii-i 

aeh>38S> loud?^^ ^eoeococi Mc{e>i94C4 

o^Ok^S eoxAoon ooci<-4or« «D^co«-4 

^«3<o<o«> fr*t«aoooa oopootot^ t<*t«r^r^i» 

! SSS3S SSSSSSS 8SSS9 SSRSS 

S90»^e« geo^fioio coooo^eo «o<DOQQ-* 

S^^fir* P^S^S ^«^»^c<« ciMclMeQ 

«4««t^ t^oeoBciOk 0'^clco-<«* tocDr«o6a» 



116 BLECTBOMAGKETS. 

is neoesiary, thiB set of tables will, of course, give the proper length, L, 
of the |>ermazient ooil. which in such cases is identical with Lt. If a oor- 
recUon in mean length is necessarv and is such as to alter materially the 
girth of the ooil, and, therefore, the radiating surface per unit of lr~ ^' 
after making the correction in mean length as explained in a precTvuuw 
pamgraph, and asoertainiiu; the calculated length of coil. L», by meanaoff 
Table III, the final value for the length (L) of the permanent ooil may be 
obtained by means of the formula 

-O ^ C2) 

O being the girth that the permanent ooil will have after oorreeting the 
mean length per turn, and Oi the girth of the test ooil. 

For convenience in making corrections in the mean length oer turn and 
the girth of the finished coil. Table IV (divided into IVa to iVe inclusive) 
has been prepared. This gives the depth of coU that will be obtained with 
different numbers of layers of the standard siiee of magnet wire, single 
and double cotton covered. 

The table is based on the insulation thicknesses used by the Roebling 
factory, and while the coil depths are given to the second and third decimal 
places, it will, of course, be understoM that this is not intended as an in- 
timation that coils can be wound in practice to any such degree of accuracy, 
even if the insulation ran absolutely uniform always, which it does not do. 
The full figures are given in this, as in Tables I and II, merely in order thi^ 
one may see what the exact theoretical values are. The table has not been 
made to include very small sixes of wire, for the reason that any approach 
to accuracy in calculations based on the insulated diameters of sudti wires 
is impossible. 

For coils wound around a continuously convex surface, such as that 
of a bobbin for a round magnet core or one of oval cross section, the mean 
length per turn of wire ia roidily obtained by means of the formula 

9 + ir d - L» (8) 

in which g is the sirth of the bobbin or former in which the ooil is wound 
and d is the depth of the winding (in inch measure,or whatever unit of 
linear measurement may be used; not in layers). The girth of the ooil 
will be obtainable by means of the formula 

a + 2»d-(? (4) 

The mean length per turn in a coil wound on a bobbin of substantially 
rectangular cross section will be greater than the value given this formula 
on account of the bulging of the wire away from the core in the parts of 
the winding which cover the straight surfaces of the bobbin or former. 
This is also true, and to a greater extent, of the girths of the finished 
coil. 



WINDING OF BLECTBOMAGNBTS. 



117 



le 



•r Magnet €)mtL 



It 










LfiDsih of Test Coil, Lu 








Ih 


U 
.96 


If 


If 


li 

1.19 


2 
1.27 


2i 
1.35 


21 
1.43 


21 
1.5 


2* 
1.58 


21 


2i 


21 


A . . 


1.03 


1.11 


1.66 


1.74 


1.82 


.425 . 


.98 


1.06 


1.14 


1.22 


1.31 


1.39 


1.47 


1.55 


1.63 


1.71 


1.8 


1.87 


.45. . 


1.01 


1.09 


1.17 


1.26 


1.34 


1.43 


1.51 


1.6 


1.68 


1.76 


1.85 


1.93 


.475 . 


1.08 


1.12 


1.21 


1.29 


1.88 


1.47 


1.55 


1.64 


1.72 


1.81 


1.9 


1.98 


J& . . 


1.06 


1.15 


1.24 


1.33 


1.42 


1.5 


1.59 


1.68 


1.77 


1.86 


1.95 


2.03 


.525 . 


1.00 


1.18 


1.27 


1.36 


1.45 


1.54 


1.63 


1.72 


1.81 


1.9 


1.99 


2.08 


.56. . 


1.12 


1.21 


1.3 


1.39 


1.48 


1.58 


1.67 


1.76 


1.86 


1.95 


2.04 


2.13 


.675 . 


1.14 


1.23 


1.33 


1.42 


1.62 


1.61 


1.71 


1.8 


1.9 


1.99 


2.09 


2.18 


.6 . . 


1.16 


1.26 


1.36 


1.45 


1.55 


1.65 


1.74 


1.84 


1.94 


2.03 


2.13 


2.23 


.625 . 


1.18 


1.29 


1.38 


1.48 


1.58 


1.68 


1.78 


1.88 


1.98 


2.08 


2.17 


2.27 


.65. . 


1.21 


1.31 


1.41 


1.51 


1.61 


1.71 


1.82 


1.92 


2.02 


2.12 


2.22 


2.32 


.675 . 


1.23 


1.34 


1.44 


1.54 


1.64 


1.76 


1.85 


1.95 


2.05 


2.16 


2.26 


2.36 


.7 . . 


1.26 


1.36 


1.47 


1.57 


1.67 


1.78 


1.88 


1.99 


2.09 


2.2 


2.3 


2.41 


.725 . 


1.28 


1.38 


1.49 


1.6 


1.7 


1.81 


1.92 


2.02 


2.13 


2.24 


2.34 


2.45 


-75 . . 


1.3 


1.41 


1.52 


1.62 


1.73 


1.84 


1.95 


2.06 


2.17 


2.27 


2.38 


2.49 


.8 . . 


1.34 


1.46 


1.57 


1.68 


1.79 


1.9 


2.01 


2.13 


2.24 


2.36 


2.46 


2.57 


.65. . 


1.30 


1.5 


1.61 


1.73 


1.85 


1.96 


2.08 


2.19 


2.31 


2.42 


2.54 


2.66 


-9 . . 


1.42 


1.54 


1.66 


1.78 


1.9 


2.02 


2.14 


2.25 


2.37 


2.49 


2.61 


2.73 


.95. . 


1.46 


1.58 


1.71 


1.83 


1.95 


2.07 


2.19 


2.32 


2.44 


2.56 


2.68 


2.8 


1. . . . 


1.5 


1.63 


1.75 


1.88 


2. 


2.13 


2.25 


2.38 


2.5 


2.63 


2.75 


2.88 


1.05. . 


1.54 


1.67 


1.79 


1.92 


2.06 


2.18 


2.31 


2.44 


2.56 


2.69 


2.82 


2.95 


l.l . . 


1.67 


1.71 


1.84 


1.97 


2.1 


2.23 


2.36 


2.40 


2.62 


2.75 


2.88 


3.02 


1.2 . . 


1.64 


1.78 


1.92 


2.05 


2.19 


2.33 


2.47 


2.6 


2.74 


2.88 


3.01 


3.15 


K3 . . 


1.71 


1.85 


1.99 


2.14 


2.28 


2.42 


2.57 


2.71 


2.85 


3. 


3.14 


3.28 


1.4 . . 


1.78 


1.92 


2.07 


2.22 


2.37 


2.51 


2.66 


2.81 


2.96 


3.11 


3.25 


3.4 


1-5 . . 


1.84 


1.99 


2.14 


2.8 


2.45 


2.6 


2.76 


2.91 


3.06 


3.22 


3.37 


3.52 


1.6 . . 


1.0 


2.06 


2.21 


2.37 


2.53 


2.69 


2.85 


3.01 


3.16 


3.32 


3.48 


3.64 


1.7 . . 


1.06 


2.12 


2.28 


2.45 


2.61 


2.77 


2.93 


3.1 


3.26 


3.42 


3.59 


3.75 


1.8 . . 


2.01 


2.18 


2.35 


2.52 


2.68 


2.85 


3.02 


3.19 


3.35 


3.52 


3.69 


3.86 


1-9 . . 


2.07 


2.24 


2.41 


2.59 


2.76 


2.93 


3.1 


3.27 


3.45 


3.62 


8.79 


3.96 


2. . . . 


2.12 


2.3 


2.48 


2.65 


2.83 


3. 


3.18 


3.36 


3.54 


3.71 


8.89 


4.07 


2.1 . . 


2.17 


2.36 


2.54 


2.72 


2.9 


3.08 


3.26 


3.44 


3.62 


3.81 


3.90 


4.17 


2.2 . . 


2.23 


2.41 


2.6 


2.78 


2.97 


3.15 


3.34 


3.52 


3.71 


3.89 


4.08 


4.27 


2.3 . . 


2.28 


2.47 


2.65 


2.84 


3.03 


3.22 


3.41 


3.6 


3.79 


3.98 


4.17 


4.36 


2.4 . . 


2.32 


2.52 


2.71 


2.91 


3.1 


3.29 


3.49 


3.68 


3.87 


4.07 


4.26 


4.46 



The Above numbers (in the body of the table) are oorrected lengths, Zc 



118 



ELECTROMAGNETS. 



Tal»le mb.— ff^r carvecttnc 



of Mac^et Call* 




It 


Length of Test Coil. Ll 


Ih 


3 

1.9 


3i 

1.98 


3i 
2.06 


31 

2.14 


3* 

2.22 


31 

2.3 


3i 
2.37 


31 


4 


4t 


4i 


41 


.4 . . 


2.45 


2.63 


2.61 


2.00 


2.77 


.425 . 


1.96 


2.04 


2.12 


2.2 


2.28 


2.36 


2.45 


2.53 


2.61 


2.60 


2.77 


2.85 


.45 . . 


2.01 


2.1 


2.18 


2.26 


2.35 


2.43 


2.52 


2.6 


2.68 


2.77 


2.85 


2.04 


.475 . 


2.07 


2.15 


2.24 


2.33 


2.41 


2.5 


2.58 


2.67 


2.76 


2.84 


2.03 


3.02 


.5 . . 


2.12 


2.21 


2.3 


2.39 


2.48 


2.56 


2.65 


2.74 


2.83 


2.92 


3.01 


3.00 


.525 . 


2.18 


2.26 


2.36 


2.45 


2.54 


2.63 


2.72 


2.81 


2.9 


2.90 


3.08 


3.17 


.55 . . 


2.23 


2.32 


2.41 


2.5 


2.60 


2.69 


2.78 


2.87 


2.97 


3.06 


3.15 


3.28 


.576 . 


2.28 


2.37 


2,46 


2.56 


2.65 


2.75 


2.84 


2.94 


3.03 


3.13 


3.22 


3.31 


.6 . . 


2.32 


2.42 


2.52 


2.62 


2.71 


2.81 


2.91 


3. 


3.1 


3.2 


3.20 


3.30 


.625 . 


2.37 


2.47 


2.57 


2.67 


2.77 


2.87 


2.97 


3.06 


3.16 


3.26 


3.36 


3.40 


.65 . . 


2.42 


2.52 


2.62 


2.72 


2.82 


2.92 


3.02 


3.13 


3.23 


3.83 


3.43 


3.53 


.675 . 


2.46 


2.57 


2.67 


2.77 


2.88 


2.98 


3.08 


3.19 


3.29 


3.30 


3.40 


3.50 


.7 . . 


2.51 


2.62 


2.72 


2.82 


2.93 


3.03 


3.14 


3.24 


3.35 


3.45 


3.56 


3.66 


.725 . 


2.56 


2.66 


2.77 


2.87 


2.98 


3.09 


3.19 


3.3 


3.41 


3.51 


3.62 


3.73 


.75 . . 


2.6 


2.71 


2.81 


2.92 


3.03 


3.14 


3.25 


8.36 


3.46 


3.57 


3.68 


3.70 


.8 . . 


2.68 


2.8 


2.91 


3.02 


3.13 


3.24 


3.35 


8.47 


8.68 


3.60 


3.8 


3.01 


.85 . . 


2.77 


2.88 


3. 


8.11 


3.23 


3.34 


3.46 


3.57 


8.69 


3.81 


3.02 


4.03 


.9 . . 


2.84 


2.97 


3.09 


3.2 


3.32 


3.44 


3.56 


3.68 


3.8 


3.01 


4.03 


4.15 


.06 . . 


2.92 


3.05 


3.17 


3.29 


3.41 


3.53 


3.66 


3.78 


3.9 


4.02 


4.14 


4.26 


1. . . . 


3. 


3.13 


3.25 


3.38 


3.5 


3.63 


3.75 


8.88 


4. 


4.13 


4.25 


4.38 


1.05 . . 


3.07 


3.2 


8.33 


8.46 


l:t? 


3.72 


3.84 


3.97 


4.1 


4.23 


4.36 


4.48 


1.1 . . 


3.14 


3.28 


3.41 


8.54 


3.8 


3.93 


4.06 


4.2 


4.38 


4.46 


4.60 


1.15 . . 


3.21 


3.35 


3.49 


3.62 


3.75 


3.89 


4.02 


4.16 


4.29 


4.42 


4.56 


4.60 


1.2 . . 


3.28 


3.44 


3.58 


3.72 


3.85 


3.99 


4.13 


4.27 


4.4 


4.54 


4.68 


4.82 


1.25 . . 


3.35 


3.49 


3.63 


3.77 


3.91 


4.05 


4.19 


4.33 


4.47 


4.61 


4.75 


4.80 


1.3 . . 


8.42 


3.56 


3.71 


3.85 


8.99 


4.13 


4.28 


4.42 


4.56 


4.7 


4.85 


4.00 


1.35 . . 


3.49 


3.63 


3.78 


3.92 


4.07 


4.21 


4.36 


4.5 


4.65 


4.79 


4.04 


5.08 


1.4 . . 


3.55 


3.7 


3.85 


3.99 


4.14i4.29 


4.44 


4.59 


4.73 


4.88 


5.03 


5.18 


1.45 . . 


3.61 


3.76 


3.91 


4.07 


4.22:4.37 


4.52 


4.67 


4.82 


4.97 


5.12 


6.27 


1.5 . . 


3.67 


3.83 


3.98 


4.13 


4.29 


4.44 


4.59 


4.75 


4.9 


5.05 


6.21 


5.30 


1.6 . . 


3.85 


3.95 


4.11 


4.27 


4.43 


4.59 


4.75 


4.9 


5.06 


5.22 


6.38 


5.53 


1.7 . . 


3.91 


4.08 


4.24 


4.4 


4.56 


4.73 


4.89 


5.05 


5.22 


5.38 


5.54 


5.71 


1.8 . . 


4.02 


4.19 


4.36 


4.53 


4.7 


4.86 


5.03 


5.2 


5.37 


5.54 


5.7 


5.87 


1.9 . . 


4.14 


4.31 


4.48 


4.65 


4.83 


6. 


5.17 


5.34 


5.51 


5.09 


6.86 


6.03 


2. . . . 


4.25 


4.42 


4.6 


4.77 


4.95 


5.13 


5.31 


5.48 


5.66 


5.83 


6.01 


0.10 



The above numbers (in the body of the table) are corrected lengthB, Lc 



^ 



mSDISQ OF BLEGTROMAOirETS. 



119 



Tabl« me. — For correcilnr IiCBi^tli of IHagvot Coll. 



/( 


length of Test Coil, Lu 


Ik 


4* 

3.18 


41 

3.27 


41 

3.36 


4i 

3.45 


6 
3.64 


5i 
3.62 


6i 
3.71 


61 

3.8 


5i 


61 


6} 
4.07 


61 


.5 . . 


3.89 


3.98 


4.16 


.525 . 


3.26 


3.35 


3.44 


3.53 


3.62 


3.71 


3.81 


3.9 


3.99 


4.08 


4.17 


4.26 


.55. . 


3.34 


3.43 


3.52 


3.62 


3.71 


3.8 


3.9 


3.99 


4.08 


4.17 


4.27 


4.36 


.575 . 


3.41 


3.51 


3.6 


3.7 


3.79 


3.89 


3.98 


4.08 


4.17 


4.27 


4.36 


4.46 


.6 . . 


3.49 


3.58 


3.68 


3.78 


3.87 


3.97 


4.07 


4.16 


4.26 


4.36 


4.46 


4.66 


.825 . 


3.56 


3.66 


3.76 


3.86 


3.95 


4.05 


4.15 


4.25 


4.85 


4.45 


4.56 


4.66 


.65. . 


3.63 


3.73 


3.83 


3.93 


4.03 


4.13 


4.23 


4.33 


4.43 


4.64 


4.64 


4.74 


.m . 


3.7 


3.8 


3.9 


4.01 


4.11 


4.21 


4.31 


4.42 


4.52 


4.62 


4.72 


4.83 


.7 . . 


3.77 


3.87 


3.97 


4.08 


4.18 


4.29 


4.39 


4.6 


4.6 


4.71 


4.81 


4.92 


.725 . 


3.83 


3.94 


4.04 


4.15 


4.26 


4.37 


4.47 


4.68 


4.68 


4.79 


4.9 


5.0 


.75. . 


3.9 


4.01 


4.11 


4.22 


4.33 


4.44 


4.55 


4.66 


4.76 


4.87 


4.98 


6.09 


.775 . 


4.01 


4.07 


4.18 


4.29 


4.4 


4.51 


4.62 


4.73 


4.84 


4.96 


6.06 


6.17 


.8 . . 


4.03 


4.14 


4.25 


4.36 


4.47 


4.68 


4.7 


4.81 


4.92 


6.03 


5.14 


6.25 


.825 . 


4.09 


4.2 


4.32 


4.43 


4.64 


4.66 


4.77 


4.88 


5. 


6.11 


6.22 


6.34 


.85. . 


4.15 


4.27 


4.38 


4.5 


4.61 


4.73 


4.84 


4.96 


6,07 


6.19 


6.3 


5.42 


.875 . 


4.21 


4.33 


4.44 


4.56 


4.68 


4.8 


4.91 


6.03 


5.16 


6.26 


6.38 


5.6 


.» . . 


4.27 


4.39 


4.51 


4.63 


4.74 


4.86 


4.98 


6.1 


5.22 


6.34 


6.46 


6.67 


.825 . 


4.33 


4.45 


4.67 


4.69 


4.81 


4.93 


5.05 


6.17 


5.29 


6.41 


5.63 


6.66 


.85. . 


4.39 


4.51 


4.63 


4.76 


4.87 


5, 


6.12 


6.24 


5.36 


6.48 


5.61 


6.73 


1. . . 


4.5 


4.63 


4.76 


4.88 


5. 


6.13 


6.26 


6.38 


6.5 


5.63 


6.75 


6.88 


1.05. . 


4.61 


4.74 


4.87 


5. 


5.12 


5.26 


6.38 


6.51 


6.64 


6.76 


5.89 


6.02 


1.1 . . 


4.72 


4.85 


4.98 


6.11 


5.26 


6.38 


6.61 


6.64 


6.77 


6.9 


6.03 


6.16 


1.15.-. 


4.83 


4.96 


5.09 


6.23 


5.36 


6.6 


6.63 


5.76 


6.9 


6.03 


6.17 


6.3 


1.2 . . 


4.96 


5.07 


5.2 


5.34 


6.48 


6.61 


6.76 


5.89 


6.03 


6.16 


6.3 


6.44 


1.25. . 


5.03 


5.17 


5.31 


6.46 


5.59 


5.73 


5.87 


6.01 


6.16 


6.20 


6.43 


6.57 


13 . . 


5.13 


5.27 


5.42 


6.66 


5.7 


5.84 


6.99 


6.13 


6.27 


6.41 


6.66 


6.7 


1.35. . 


5.23 


6.37 


5.52 


6.67 


5.81 


6.96 


6.1 


6.25 


6.39 


6.64 


6.68 


6.83 


1.4 . . 


5.33 


6.47 


5.62 


6.77 


5.92 


6.07 


6.21 


6.36 


6.51 


6.66 


6.81 


6.96 


1.46. . 


5.42 


5.57 


5.72 


6.87 


6.02 


6.17 


6.32 


6.47 


6.62 


6.77 


6.93 


7.08 


1.5 . . 


5.51 


5.67 


6.82 


5.97 


6.12 


6.28 


6.43 


6.58 


6.74 


6.89 


7.04 


7.2 


1.55. . 


5.6 


5.76 


5.91 


6.07 


6.23 


6.38 


6.54 


6.69 


6.86 


7. 


7.16 


7.32 


i.e . . 


5.69 


6.85 


6.01 


6.17 


6.33 


6.48 


6.64 


6.8 


6.96 


7.12 


7.27 


7.43 


1.65. . 


5.78 


6.94 


6.1 


6.26 


6.42 


6.68 


6.74 


6.91 


7,07 


7.23 


7.30 


7.66 


1.7 . . 


5.87 


6.03 


6.19 


6.36 


6.62 


6.68 


6.86 


7.01 


7.17 


7.33 


7.5 


7.66 


1.75. . 


5.96 


6.12 


6.28 


6.46 


6.61 


6.78J6.96 


7.11 


7.28 


7.44 


7.61 


7.77 


1.8 . . 


6.04 


6.21 


6.37 


6.54 


6.71 


6.88 


7.06 


7.21 


7.38 


7.55 


7.72 


7.88 


1.85. . 


6.12 


6.29 


6.46 


6.636.8 


6.97 


7.14 


7.31 


7.48 


7.65 


7.82 


7.99 


18 . . 


6.2 


6.38 


6.65 


6.72 6.89 


7.07 


7.24 


7.41 


7.68 


7.75 


7.03 


8.1 


I*- • 


6.286.46 


6.63 


6.81,6.08 


7.167.33 


7.51 


7.68 


7.86 


8.03 


8.21 


2. . . . 


6.37 6.54 


6.72 


6.9 


7.07 


7.25 7.42 


7.6 


7.78 


7.96 


8.13 


8.31 




( 



The above numbera (in the body of the table) are corrected lengths, Lc, 



120 



BLBCTB0B1A.ONBTS. 



Table md. — for corractlar I<cnMrtli of Maff»«t C«Pil. 



It 


Tipjigth of Test Coil, Lu 


Ih 


6 


6i 
4.33 


6i 
4.44 


61 
4.61 


6i 
4.6 


61 
4.69 


6i 

4.77 


61 
4.86 


7 
4.95 


7i 


7i 


71 


.6 . . 


4.24 


6.04 


6.13 


5.22 


.525 . 


4.35 


4.44 


4.63 


4.62 


4.71 


4.8 


4.80 


4.98 


5.07 


6.16 


5.26 


5.34 


.55 . . 


4.45 


4.54 


4.64 


4.73 


4.82 


4.91 


6.01 


5.1 


6.10 


5.20 


5.38 


6.47 


.575 . 


4.55 


4.65 


4.74 


4.83 


4.93 


6.02 


5.12 


5.21 


6.31 


5.4 


6.5 


5.50 


.6 . . 


4.65 


4.75 


4.84 


4.94 


5.04 


6.13 


6.23 


6.33 


6.42 


5.62 


5.62 


5.71 


.625 . 


4.75 


4.84 


4.94 


5.04 


5.14 


6.24 


6.34 


5.44 


5.53 


5.63 


5.73 


5.83 


.65 . . 


4.84 


4.04 


6.04 


5.14 


6.24 


6.84 


5.44 


5.54 


5.64 


6.76 


5.85 


5.05 


.675 . 


4.03 


5.03 


6.14 


5.24 


5.34 


6.44 


6.66 


6.65 


5.76 


5.86 


6.06 


6.06 


.7 . . 


5.02 


5.13 


6.23 


5.33 


5.44 


6.54 


5.66 


5.76 


6.86 


6.06 


6.07 


6.17 


.725 . 


6.11 


5.22 


5.32 


5.43 


6.53 


6.64 


5.76 


5.86 


6.06 


6.07 


6.17 


6.28 


.75 . . 


5.2 


5.3 


5.41 


6.52 


5.63 


6.74 


6.85 


5.05 


6.06 


6.17 


6.28 


6.30 


.775 . 


5.28 


5.30 


5.5 


5.61 


5.72 


5.83 


5.04 


6.06 


6.16 


6.27 


6.30 


6.40 


.8 . . 


5.37 


5.48 


5.69 


5.7 


5.81 


5.93 


6.04 


6.16 


6.26 


6.37 


6.40 


6.6 


.825 . 


5.45 


5.56 


5.68 


5.79 


6.91 


6.02 


6.13 


6.26 


6.36 


6.47 


6.50 


6.7 


.85 . . 


6.53 


5.65 


5.76 


6.88 


5.99 


6.11 


6.22 


6.34 


6.46 


6.67 


6.00 


6.8 


.875 . 


5.61 


5.73 


5.86 


6.96 


6.08 


6.2 


6.31 


6.43 


6.56 


6.67 


6.78 


6.0 


.9 . . 


5.60 


5.81 


5.93 


6.06 


6.17 


6.29 


6.4 


6.62 


6.64 


6.76 


6.88 


7. 


.025 . 


5.77 


5.80 


6.01 


6.13 


6.25 


6.37 


6.40 


6.61 


6.73 


6.86 


6.07 


7.00 


.05 . . 


5.85 


5.07 


6.09 


6.21 


6.34 


6.46 


6.68 


6.7 


6.82 


6.05 


7.07 


7.10 


1. . . . 


6. 


6.13 


6.25 


6.38 


6.6 


6.63 


6.76 


6.88 


7. 


7.18 


7.25 


7.38 


1.06 . . 


6.15 


6.28 


6.41 


6.53 


6.66 


6.79 


6.02 


7.05 


7.17 


7.8 


7.43 


7.66 


1.1 . . 


6.29 


6.43 


4.56 


6.69 


6.82 


6.95 


7.08 


7,21 


7.34 


7.47 


7.61 


7.74 


1 . 15 . . 


6.44 


6.57 


6.7 


6.84 


6.97 


7.11 


7.24 


7.37 


7.61 


7.64 


7.78 


7.91 


1.2 . . 


6.57 


6.71 


6.86 


6.99 


7.12 


7.26 


7.39 


7.63 


7.67 


7.81 


7.04 


8.08 


1.25 . . 


6.71 


6.85 


6.99 


7.13 


7.27 


7.41 


7.55 


7.69 


7.83 


7.07 


8.11 


8.25 


1.3 . . 


6.84 


6.08 


7.13 


7.27 


7.41 


7.66 


7.7 


7.84 


7.08 


8.13 


8.27 


8.41 


1.35 . . 


6.07 


7.12 


7.26 


7.41 


7.65 


7.7 


7.84 


7.99 


8.13 


8.28 


8.43 


8.57 


1.4 . . 


7.1 


7.25 


7.4 


7.54 


7.69 


7.84 


7.99 


8.13 


8.28 


a. 43 


8.68 


8.78 


1.45 . . 


7.23 


7.38 


7.63 


7.68 


7.83 


7.98 


8.13 


8.28 


8.43 


8.58 


8.73 


8.88 


1.5 . . 


7.35 


7.5 


7.66 


7.81 


7.96 


8.11 


8.27 


8.42 


8.67 


8.73 


8.88 


0.08 


1.55 . . 


7.47 


7.63 


7.78 


7.94 


8.09 


8.25 


8.4 


8.66 


8.72 


8.87 


0.03 


9.18 


1.6 . . 


7.50 


7.75 


7.91 


8.07 


8.22 


8.38 


8.54 


8.7 


8.86 


0.01 


0.17 


0.33 


1.65 . . 


7.71 


7.87 


8.03 


8.19 


8.35 


8.51 


8.67 


8.83 


8.00 


0.16 


0.31 


9.47 


1.7 . . 


7.82 


7.99 


8.15 


8.31 


8.48 


8.64 


8.8 


8.96 


0.13 


0.20 


0.45 


9.62 


1.75 . . 


7.04 


8.1 


8.27 


8.43 


8.6 


8.77 


8.93 


9.09 


0.26 


0.43 


0.50 


0.76 


1.8 . . 


8.05 


8.22 


8.39 


8.55 


8.72 


8.89 


9.06 


9.22 


0.30 


0.66 


0.73 


0.0 


1.85 . . 


8.16 


8.33 


8.5 


8.67 


8.84 


9.01 


9,18 


9.36 


0.52 


0.60 


0.86 


10.03 


1.0 . . 


8.27 


8.44 


8.62 


8.79 


8.96 


9.13 


9.3 


9.48 


0.66 


0.82 


0.00 


10.17 


1.06 . . 


8.38 


8.65 


8.73 


8.9 


9.08 


9.25 


9.43 


9.6 


0.78 


0.06 


10.13 


10.3 


2. . . . 


8.49 


8.66 


8.84 


9.02 


9.19 


9.37 


9.56 


9.72 


0.0 


10.08 


10.25 


10.43 



The ftbove numbers (in the body of the table) are corrected leogths, Le* 



WINDIKO OF ELECTROMAGNETS. 



121 



VaMe TVm. — lilBear flimce •ocniH*' l»7 Marl« C«ttom 



or 



2 
3 

4 
5 
6 

7 

S 

9 

10 

11 

12 
13 
14 
U 

le 

17 
18 
19 
20 
21 



24 . 

25 . 
21 . 

27 . 

28 . 

29 . 
» . 
SI . 

32 . 
S3 . 
34. 

35 . 

3S. 

37. 



41 

42 
43 
44 

45 



47 
48 

» 
52 

54 
54 
58 
60 
52 
54 



Wire Numbers, B. A 8. Gauge : 



0.432!0.388 



0.648 
0.864 
1.08 
1.296 

1.512 

1.728 

1.994 

2.16 

2.38 

2.59 
2.81 
3.03 
3.24 
3.46 

3.67 
3.89 
4.11 
4.32 
4.53 

4.76 
4.97 



0.582 
0.776 
0.97 
1.164 



358 
552 
746 
94 

14 

33 
52 
72 
91 
11 



1. 
1. 
I. 
1. 
2. 

2. 
2. 
2. 
2. 
3. 

3.3 

3.49 

3.69 

3.88 

4.07 

4.27 
4.46 
4.65 
4.85 
5.06 






0.344 

0.516 

0.688 

0.86 

1.032 



1. 
1. 
1. 
1. 
1. 

2. 
2. 
2. 
2. 
2. 

2. 
8. 
3. 
3. 
3. 

3. 
3 

4 
4 
4 

4 
4 
4 
5 



204 

376 

548 

72 

89 

07 
24 
41 
58 
75 

93 
1 

27 
44 

61 

.78 

.95 

.125 

.3 

.47 

.64 
.81 
.98 
.16 



0.308 

0.462 

0.616 

0.77 

0.924 

1.078 

1.232 

1.386 

1.54 

1.69 

1.85 

2. 

2.16 

2.31 

2.47 

2.62 
2.77 
2.93 
3.08 
3.24 

3.89 
3.54 
3.69 
3.85 
4. 

4.16 
4.31 
4.46 
4.62 

4.77 

4.98 
5.08 



8 



9 



0.274 
0.411 
0.548 
0.685 
0.822 

0.959 

1.096 

1.233 

1.37 

1.51 

1.64 
1.78 
1.92 
2.06 
2.19 

2.33 
2.47 
2.61 
2.74 
2.88 

3.02 
3.15 
3.29 
3.43 
3.56 

3.7 
3.83 
3.97 
4.11 
25 

38 
52 
65 
79 
93 



.69 
.81 
.93 
3.05 
3.17 



5.07 



0.244 

0.366 

0.488 

0.61 

0.732 

0.854 

0.976 

1.098 

1.22 

1.34 

1.47 
1.59 
1.71 
1.83 
1.95 

2.06 

2.2 

2.32 

2.44 

2.56 



29 
41 
54 
66 
78 



3.9 

4.02 

4.14 

4.27 

4.39 



.51 
.63 
4.76 
4.88 
5. 



10 



0.216 

0.324 

0.432 

0.54 

0.648 

0.756 

0.864 

0.972 

1.08 

1.19 

1.3 

1.41 

1.51 

1.62 

1.73 

1.84 
1.95 
2.05 
2.16 
2.27 

2.38 

2.49 

2.59 

2.7 

2.81 

2.92 
3.03 
3.13 
3.24 
3.35 

3.45 
3.56 
3.67 
3.78 
3.89 

3.99 

4.1 

4.21 

4.32 

4.42 



.53 
.64 
4.75 
4.86 
4.97 



11 



0.194 
0.291 
0.388 
0.485 
0.582 

0.679 

0.776 

0.873 

0.97 

1.07 

1.17 
1.26 
1.36 
1.46 
1.55 

1.65 
1.75 
1.85 
1.94 
2.04 

2.14 
2.23 
2.33 
2.43 
2.52 

2.62 
2.72 
2.82 
2.91 
3. 

3.1 

3.2 

3.29 

3.39 

3.49 

3.59 
3.68 
8.78 
3.88 
3.97 

4.07 
4.17 
4.27 
4.36 
4.46 



.56 
.66 
4.76 
4.85 



12 



0.174 
0.261 
0.348 
0.435 
0.522 

0.609 

0.606 

0.783 

0.87 

0.96 

1.05 
1.13 
1.22 
1.31 
1.39 

1.48 
1.67 
1.66 
1.74 
1.83 

1.92 

2. 

2.09 

2.18 

2.26 

2.35 
2.44 
2.53 
2.61 
2.7 

2.79 
2.87 
2.96 
3.04 
3.13 

3.22 

3.3 

3.39 

3.48 

3.56 

3.65 
3.74 
3.83 
3.91 
4. 

4.09 
4.18 
4.27 
4.35 
4.52 

4.7 
4.87 



13 



0.16 
0.24 
0.31 
0.39 
0.47 

0.55 
0.63 
0.70 
0.78 
0.86 

0.94 
1.02 
1.09 
1.17 
1.25 

1.83 

1.44 
1.48 
1.56 
1.64 

1.72 

1.8 

1.87 

1.95 

2.03 

2.11 
2.19 
2.26 
2.34 
2.42 

2.5 

2.58 

2.65 

2.73 

2.81 

2.89 
2.97 
3.04 
3.12 
3.2 

3.27 
3.35 
3.43 
3.51 
3.59 

3.66 
3.74 
3.82 
3.95 
4.06 

4.22 
4.37 
4.52 
4.68 



14 

oTii 

0.21 
0.28 
0.35 
0.42 

0.49 

0.56 

0.63 

0.7 

0.77 

0.84 
0.01 
.98 
1.05 
1.12 

1.19 
1.26 
1.33 

1.4 
1.47 

1.54 
1.61 
1.68 
1.75 
1.82 

1.89 

1.96 

2.03 

2.1 

2.17 

2.24 
2.31 
2.38 
2.45 
2.52 

2.59 

2.66 

2.73 

2.8 

2.87 



2.04 
3.01 
3.08 
3.15 
3.22 

3.29 

3.36 

3.43 

3.6 

3.64 

3.78 

3.92 

4.06 

4.2 

4.34 

4.48 



122 



ELEGTBOMAONBTS. 






Turns or 


Wire Numben. B. & 8. Gauge: 


Layers. • 


15 . 


16 


17 


18 


19 


20 


21 


22 


23 


24 


6. . . . 


0.38 


0.34 


0.31 


0.28 


0.25 


0.23 


0.2 


0.19 


0.17 


' O.U 


7. . . . 


0.44 


0.4 


0.36 


0.32 


0.29 


0.27 


0.24 


0.22 


0.2 


0.17 


8. . . . 


0.5 


0.46 


0.41 


0.37 


0.34 


0.8 


0.27 


0.25 


0.22 


\ 0.2 


9. . . . 


0.57 


0.51 


0.46 


0.41 


0.38 


0.34 


0.81 


0.28 


0.25 


> 0.21 


10. . . . 


0.63 


0.57 


0.51 


0.46 


0.42 


0.38 


0.34 


0.31 


0.28 


E 0.2i 


11 ... . 


0.69 


0.63 


0.56 


0.61 


0.46 


0.42 


0.37 


0.34 


0.81 


0.27 


12. . . . 


0.76 


0.68 


0.61 


0.56 


0.5 


0.46 


0.41 


0.37 


0.34 


0.8 


13 ... . 


0.82 


0.74 


0.66 


0.6 


0.55 


0.49 


0.44 


0.4 


0.36 


0.33 


14 ... . 


0.88 


0.8 


0.71 


0.64 


0.59 


0.63 


0.48 


0.43 


0.30 


0.3C 


16 ... . 


0.96 


0.85 


0.76 


0.69 


0.63 


0.67 


0.61 


0.46 


0.42 


0.38 


16 


1.01 


0.91 


0.82 


0.74 


0.67 


0.61 


0.64 


0.6 


0.46 


0.4 


17 ... . 


1.07 


0.97 


0.87 


0.78 


0.72 


0.65 


0.68 


0.68 


0.48 


0.42 


18. . . . 


1.13 


1.03 


0.92 


0.83 


0.76 


0.68 


0.61 


0.66 


0.6 


0.46 


19 ... . 


1.2 


1.08 


0.97 


0.87 


0.8 


0.72 


0.66 


0.69 


0.63 


0.47 


20 ... . 


1.26 


1.14 


1.02 


0.92 


0.84 


0.76 


0.68 


0.62 


0.56 


0.6 


21 ... . 


1.32 


1.2 


1.07 


0.97 


0.88 


0.8 


0.71 


0.65 


0.69 


0.52 


22 ... . 


1.39 


1.25 


1.12 


1.01 


0.92 


0.84 


0.75 


0.68 


0.62 


0.56 


23. . . . 


1.45 


1.31 


1.17 


1.06 


0.97 


0.87 


0.78 


0.71 


0.64 


0.57 


24 ... . 


1.51 


1.37 


1.22 


1.1 


1.01 


0.91 


0.82 


0.74 


0.67 


0.6 


25 ... . 


1.57 


1.42 


1.27 


1.15 


1.05 


0.95 


0.86 


0.78 


0.7 


0.62 


26. . . . 


1.64 


1.48 


1.33 


1.2 


1.09 


0.99 


0.88 


0.81 


0.73 


0.65 


27 ... . 


1.7 


1.54 


1.38 


1.24 


1.13 


1.03 


0.92 


0.84 


0.76 


0.67 


28. . . . 


1.76 


1.6 


1.43 


1.29 


1.18 


1.06 


0.95 


0.87 


0.78 


0.7 


29. . . . 


1.83 


1.65 


1.48 


1.33 


1.22 


1.1 


0.99 


0.9 


0.81 


0.72 


30 ... . 


1.89 


1.71 


1.53 


1.38 


1.26 


1.14 


1.02 


0.93 


0.84 


0.75 


31 ... . 


1.95 


1.77 


1.58 


1.43 


1.3 


1.18 


1.05 


0.96 


0.87 


0.77 


32 ... . 


2.02 


1.82 


1.63 


1.47 


1.34 


1.22 


1.09 


0.99 


0.9 


0.8 


33 ... . 


2.08 


1.88 


1.68 


1.52 


1.39 


1.25 


1.12 


1.02 


0.98 


0.82 


34 ... . 


2.14 


1.94 


1.73 


1.56 


1.43 


1.29 


1.16 


1.06 0.96 


0.85 


35. . . . 


2.2 


2. 


1.78 


1.61 


1.47 


1.33 


1.19 


1.08 


0.98 


0.87 


36. . . . 


2.27 


2.05 


1.84 


1.66 


1.51 


1.37 


1.22 


1.12 


1.01 


0.9 


37 ... . 


2.33 


2.11 


1.89 


1.7 


1.56 


1.41 


1.26 


1.16 


1.04 


0.92 


38 ... . 


2.39 


2.17 


1.94 


1.75 


1.6 


1.44 


1.29 


1.18 


1.06 


0.95 


39 ... . 


2.46 


2.22 


1.99 


1.79 


1.64 


1.48 


1.33 


1.21 


1.09 


0.97 


40 ... . 


2.52 


2.28 


2.04 


1.84 


1.68 


1.52 


1.36 


1.24 


1.12 


1. 


41 ... . 


2.58 


2.34 


2.09 


1.89 


1.72 


1.66 


1.89 


1.27 


1.15 


1.02 


42 ... . 


2.65 


2.39 


2.14 


1.93 


1.76 


1.6 


1.43 


1.8 


1.18 


1.05 


43 ... . 


2.71 


2.45 


2.19 


1.98 


1.81 


1.63 


1.46 


1.83 


1.2 


1 .07 


44 ... . 


2.77 


2.51 


2.24 


2.02 


1.85 


1.67 


1.5 


1.36 


1.23 


1.1 


45 ... . 


2.83 


2.56 


2.29 


2.07 


1.89 


1.71 


1.63 


1.89 


1.26 


1.12 


46 ... . 


2.9 


2.62 


2.35 


2.12 


1.93 


1.75 


1.66 


1.43 


1.29 


1.15 


47 ... . 


2.96 


2.68 


2.4 


2.16 


1.97 


1.79 


1.6 


1.46 


1.32 


1.17 


48 ... . 


3.02 


2.73 


2.45 


2.21 


2.02 


1.82 


1.63 


1.49 


1.34 


1.2 


49 ... . 


3.09 


2.79 


2.5 


2.25 


2.06 


1.86 


1.67 


1.62 


1.37 


1.22 


60 ... . 


3.15 


2.85 


2.55 


2.3 


2.1 


1.9 


1.7 


1.66 


1.4 


1.25 


62 ... . 


3.27 


2.96 


2.65 


2.39 


2.18 


1.98 


1.77 


1.61 


1.46 


1.8 


54 ... . 


3.4 


3.08 


2.75 


2.48 


2.27 


2.05 


1.84 


1.67 


1.61 


1.35 


56 ... . 


3.53 


3.19 


2.86 


2.58 


2.35 


2.13 


1.9 


1.74 


1.67 


1.4 


58 ... . 


3.65 


3.31 


2.96 


2.67 


2.44 


2.2 


1.97 


1.8 


1.62 


1.45 


60 ... . 


3.78 


3.42 


3.06 


2.76 


2.52 


2.28 


2.04 


1.86 


1.68 


1.5 


62 ... . 


3.91 


3.53 


3.16 


2.85 


2.6 


2.36 


2.11 


1.92 


1.74 


1.55 


64 ... . 


4.03 


3.65 


3.26 


2.94 


2.69 


2.43 


2.18 


1.98 


1.79 


1.0 


66 ... . 


4.16 


3.76 


3.37 


3.04 


2.77 


2.51 


2.24 


2.06 


1.85 


1.65 


68 ... . 


4.28 


3.88 


3.47 3.13 


2.86 2.58 


2.31 


2.11 


1.9 


1.7 


70 ... . 


4.41 3.99 


3.57 3.22 


2.94 2.66 2.381 


2.17 


1.96 


1.75 



WINDING OF ELECTROMAGNETS. 



123 



^ 










Wire Numbers, 


B. A S. 


Gauge: 






Turns or 


















Lftyen. 




















17 


18 


19 


20 


21 


22 


23 


24 


72 


3.67 


3.31 


3.02 


2.74 


2.45 


2.23 


2.02 


1.8 


74 


3.77 


3.4 


3.11 


2.81 


2.52 


2.29 


2.07 


1.85 


76 


3.88 


3.6 


3.19 


2.89 


2.58 


2.36 


2.13 


1.9 


78 


3.98 


3.58 


3.28 


2.96 


2.65 


2.42 


2.18 


1.95 


SO 


4.08 


3.68 


3.36 


3.04 


2.72 


2.48 


2.24 


2. 


82 


4.18 


3.77 


3.44 


3.12 


2.79 


2.54 


2.3 


2.05 


84 


4.28 


8.86 


3.53 


3.19 


2.86 


2.6 


2.35 


2.1 


86 


4.39 


3.96 


3.61 


3.27 


2.92 


2.67 


2.41 


2.15 


88 


4.49 


4.05 


3.7 


3.34 


2.99 


2.73 


2.46 


2.2 


» 


4.59 


4.14 


3.78 


3.42 


3.06 


2.79 


2.52 


2.25 


82 




4.23 


3.86 


3.5 


3.13 


2.85 


2.58 


2.3 


M 




4.32 


3.95 


3.57 


3.2 


2.91 


2.63 


2.35 


W 




4.42 


4.03 


3.65 


3.26 


2.98 


2.69 


2.4 


88 




4.51 


4.12 


3.72 


3.33 


3.04 


2.74 


2.45 


100 




4.6 


4.2 


3.8 


3.4 


3.1 


2.8 


2.5 


102 




■ • ■ • 


4.28 


3.88 


3.47 


3.16 


2.86 


2.55 






■ « « • 


4.37 


3.95 


3.54 


3.22 


2.91 


2.6 


106 




.... 


4.45 


4.08 


3.6 


3.29 


2.97 


2.65 






• • • • 


4.54 


4.1 


3.67 


3.35 


3.02 


2.7 


no 




• « ■ • 


• • • ■ 


4.18 


3.74 


3.41 


3.08 


2.75 


112 




• • • • 




4.26 


3.81 


3.47 


3.14 


2.8 






« • • • 




4.33 


3.88 


3.53. 


3.19 


2.85 


116 




• • • • 




4.41 


3.94 


3.6 


3.25 


2.9 






• • • • 




4.48 


4.01 


3.66 


3.3 


2.95 


120 




» • ■ « 


.... 


4.56 


4.08 


3.72 


3.36 


3. 



lE^aUe ITd. — IJ»«»r Jlpa«e occajpled Iby ]>oabIe Cottom- 



Ccvrered 'Wfre». 





Wire Numbers, B. dc S. Gauge: 


1)uDsor 




Uy«ra. 


























4 


5 
0.4 


6 


7 
0.32 


8 


9 


10 


11 


12 


13 
0.16 


14 


2. . . 


0.444 


0.356 


0.284 


0.252 


0.224 


0.202 


0.182 


0.15 


3. . . 


0.066 


0.6 


0.534 


0.48 


0.426 


0.378 


0.336 


0.303 


0.273:0.24 


0.22 


4. . . 


0,888 


0.8 


0.712 


0.64 


0.568 


0.504 


0.448 


0.404 


0.364 0.32 


0.29 


5- . . 


1.11 


1. 


0.89 


0.8 


0.71 


0.63 


0.56 


0.505 


0.455 0.4 


0.36 


8. . . 


1.332 


1.2 


1.068 


0.96 


0.852 


0.756 


0.672 


0.606 


0.546 


0.49 


0.44 


!■• • 


1.554 


1.4 


1.246 


1.12 


0.994 


0.882 


0.784 


0.707 


0.637 


0.57 


0.51 


8. . . 


1.776 


1.6 


1.424 


1.28 


1.136 


1.008 


0.896 


0.808 


0.728 


0.650.58 


^l■ • • 


1.998 


1.8 


1.602 


1.44 


1.278 


1.134 


1.008 


0.909 


0.819 


0.730.66 


?• • • 


2.22 


2. 


1.78 


1.6 


1.42 


1.26 


1.12 


1.01 


0.91 


0.8110.73 


11. . . 


2.442 


2.2 


1.958 


1.76 


1.562 1.386 

i 


1.232 


1.111 


1.001 


0.89.0.8 




{ 






ELEGTROMAONETS. 



"MAmmmr Space occupied by lieable 
Gorered ITire*. — OmftfUMd. 



Turns or 
Layers. 



12. 
13. 
14. 
15. 
16. 

17. 

18. 

19. 

20 

21. 

22. 
23. 
24. 
25. 
26. 

27. 
28. 
29. 
30. 
31. 

32. 
33. 
34. 
35. 
36. 



37. 
38. 
89. 
40. 
41. 

42. 
43. 
44. 
45. 
46. 

47. 
48. 
48. 
50. 
52. 

54. 
56. 
58. 
60. 
62. 



Wire Numbers, B. A 8. Gauge: 



2.664 

2.886 

3.108 

3.33 

3.55 

3.77 

4. 

4.22 

4.44 

4.66 

4.88 



2.4 

2.6 

2.8 

3. 

3.2 

3.4 

3.6 

3.8 

4. 

4.2 

4.4 
4.6 
4.8 
5. 



6 



2.136 

2.314 

2.492 

2.67 

2.85 

3.03 

3.2 

3.38 

3.56 

3.74 

3.92 
4.09 
4.27 
4.45 
4.63 

4.81 
4.98 



1.92 

2.08 

2.24 

2.4 

2.56 

2.72 

2.88 

3.04 

3.2 

3.36 

3.52 

3.68 

3.84 

4. 

4.16 

4.32 

4.48 
4.64 
4.8 
4.96 



8 



1.704 

1.846 

1.988 

2.13 

2.27 

2.41 
2.56 
2.77 
2.84 
2.98 

3.12 
3.27 
3.41 
3.55 
3.69 

3.83 

3.98 

4.12 

4.2 

4.4 

4.54 
4.6 
4.8 
4.97 



9 



1.512 

1.638 

1.764 

1.89 

2.01 

2.14 
2.27 
2.39 
2.52 
2.65 

2.77 

2.9 

3.02 

3.15 

3.28 

3.4 

3.53 

3.65 

3.78 

3.91 

4.03 
4.16 
4.28 
4.41 
4.54 

4.66 
4.79 
4.91 
5.04 



10 



1.344 

1.456 

1.568 

1.68 

1.79 

1.9 

2.02 

2.13 

2.24 

2.35 

2.46 

2.58 

2.09 

2.8 

2.91 

3.02 
3.14 
3.25 
3.36 
3.47 

3.58 

3.7 

3.81 

3.92 

4.03 

4.14 
4.26 
4.37 
4.48 
4.59 

4.7 
4.82 
4.93 
5.04 



11 



1.212 

1.313 

1.414 

1.51 

1.62 

1.72 
1.82 
1.92 
2.02 
2.12 

2.22 
2.32 
2.42 
2.53 
2.63 

2.73 
2.88 
2.93 
3.03 
3.13 

3.23 
3.33 
3.43 
3.54 
3.64 

3.74 
3.84 
3.94 
4.04 
4.14 

4.24 
4.34 
4.44 
4.55 
4.66 

4.76 
4.85 



12 



1.002 

1.183 

1.274 

1.36 

1.46 

1.55 
1.64 
1.73 
1.82 
1.91 

2. 

2.09 

2.18 

2.28 

2.37 

2.46 
2.55 
2.64 
2.73 
2.82 

2.91 

3. 

3.00 

3.19 

8.28 

3.87 
3.46 
3.55 
3.64 
8.78 

3.82 

3.91 

4. 

4.1 

4.19 

4.28 
4.37 
4.46 
4.55 
4.73 

4.91 



13 



0.97 
1.05 
1.13 
1.21 
1.3 

1.38 
1.46 
1.54 
1.62 
1.7 

1.78 
1.86 
1.94 
2.03 
2.11 

2.19 
2.27 
2.35 
2.43 
2.61 



14 



2.50 
2.67 
2.76 
2.84 
2.02 

3. 

3.08 

3.16 

3.24 

3.32 

3.4 

3.48 

3.56 

3.65 

3.73 

3. '81 
3.89 
3.97 
4.05 
4.21 

4.37 
4.54 
4.7 
4.86 



0.88 

0.95 

1.02 

l.J 

1.17 

1.24 

1.31 
1.88 
1.46 
1.53 

1.61 
1.68 
1.75 
1.88 
1.9 

1.97 
2.04 
2.12 
2.19 
2.26 

2.34 
2.41 
2.48 
2.56 
2.63 

2.7 

2.77 

2.85 

2.92 

2.99 

3.07 
3.14 
3.21 
3.29 
3.36 

3.48 

3.5 

3.58 

3.65 

3.82 



3.94 
4.00 
4.23 
4.86 
4.58 



WINDING OF BLECTKOMAaNETS. 



126 



IWUe IVe.— UMcai* Space occupied 1»y ]»oiilile G«tt«m 









Wire Numbers 


, B. and S. Gauce: 




Tumor 


















Uyen. 
























15 


16 


17 


18 


10 


20 


21 


22 


23 


24 


7. . . . 


0.46 


0.42 


0.38 


0.35 


0.32 


0.20 


0.26 


0.24 


0.22 


0.2 


8. . . . 


0.53 


0.48 


0.48 


0.4 


0.36 


0.83 


0.3 


0.27 


0.25 


0.23 


• • . . . 


0.50 


0.54 


0.40 


0.45 


0.4 


0.37 


0.34 


0.31 


0.28 


0.26 


M. . . . 


0.66 


0.6 


0.54 


0.5 


0.45 


0;41 


0.37 


0.34 


0.31 


0.28 


11. . . . 


0.73 


0.66 


0.50 


0.55 


0.5 


0.45 


0.41 


0.38 


0.34 


0.31 


a. . . . 


0.79 


0.72 


0.65 


0.50 


0.54 


0.40 


0.45 


0.41 


0.37 


0.34 


13. . . . 


0.86 


0.78 


0.71 


0.65 


0.50 


0.53 


0.40 


0.44 


0.41 


0.37 


14. . . . 


0.92 


0.84 


0.76 


0.60 


0.63 


0.58 


0.53 


0.48 


0.43 


0.30 


15. .*. . 


0.00 


0.0 


0.81 


0.74 


0.68 


0.62 


0.56 


0.51 


0.47 


0.42 


18. . . . 


1.06 


0.06 


0.86 


0.70 


0.72 


0.66 


0.6 


0.54 


0.5 


0.45 


17. . . . 


1.12 


1.02 


0.02 


0.84 


0.77 


0.7 


0.64 


0.58 


0.53 


0.48 


18. . . . 


1.10 


1.08 


0.07 


0.80 


0.81 


0.74 


0.86 


0.61 


0.56 


0.51 


19. . . . 


1.25 


1.14 


1.03 


0.04 


0.86 


0.78 


0.71 


0.65 


0.59 


0.53 


». . . . 

At 


1.32 


1.2 


1.08 


0.00 


0.0 


0.82 


0.75 


0.68 


0.62 


0.56 


21. . . . 


1.30 


1.26 


1.13 


1.04 


0.05 


0.86 


0.70 


0.72 


0.65 


0.50 


2. . . . 


1.46 


1.32 


1.10 


1.00 


0.00 


0.0 


0.83 


0.75 


0.68 


0.62 


23. . . . 


1.52 


1.38 


1.24 


1.14 


1.04 


0.04 


0.86 


0.78 


0.72 


0.65 


M. . . . 


1.58 


1.44 


1.3 


1.10 


1.08 


0.08 


0.0 


0.82 


0.75 


0.67 


25. . . . 


1.65 


1.5 


1.35 


1.24 


1.13 


1.03 


0.04 


0.85 


0.78 


0.7 


24. . . . 


1.72 


1.56 


1.4 


1.20 


1.17 


1.07 


0.08 


0.88 


0.81 


0.78 


27. . . . 


1.78 


1.62 


1.46 


1.84 


1.22 


1.11 


1.01 


0.92 


0.84 


0.76 


28. . . . 


1.85 


1.68 


1.51 


1.30 


1.26 


1.15 


1.05 


0.95 


0.87 


0.70 


29- . . . 


1.01 


1.74 


1.57 


1.44 


1.31 


1.19 


1.00 


0.99 


0.9 


0.81 


30. . . . 

ikft 


1.08 


1.8 


1.62 


1.40 


1.35 


1.23 


1.13 


1.02 


0.93 


0.84 


31. . . . 


2.06 


1.86 


1.68 


1.54 


1.4 


1.27 


1.16 


1.06 


0.96 


0.87 


32. . . . 


2.11 


1.02 


1.73 


1.58 


1.44 


1.31 


1.2 


1.09 


0.99 


0.0 


33. . . . 


2.18 


1.08 


1.78 


1.63 


1.40 


1.36 


1.24 


1.12 


1.02 


0.02 


3*. . . . 

A* 


2.25 


2.04 


1.84 


1.68 


1.53 


1.4 


1.28 


1.16 


1.05 


0.05 


35. . . . 


2.31 


2.1 


1.80 


1.73 


1.58 


1.44 


1.31 


1.19 


1.09 


0.08 


38. . . . 


2.38 


2.16 


1.05 


1.78 


1.62 


1.48 


1.35 


1.23 


1.12 


1.01 


37. . . . 


2.44 


2.22 


2. 


1.83 


1.67 


1.52 


1.30 


1.26 


1.15 


1.04 


38. . . . 


2.61 


2.28 


2.06 


1.88 


1.71 


1.56 


1.43 


1.29 


1.18 


1.07 


38- . . . 


2.58 


2.84 


2.11 


1.03 


1.76 


1.6 


1.46 


1.33 


1.21 


1.00 


*. . . 


2.64 


2.4 


2.16 


1.08 


1.8 


1.64 


1.5 


1.36 


1.24 


1.12 


41. . . ". 


2.71 


2.46 


2.22 


2.03 


1.85 


1.68 


1.54 


1.4 


1.27 


1.15 


42. . . . 

JA 


2.77 


2.52 


2.27 


2.08 


1.80 


1.72 


1.58 


1.43 


1.3 


1.18 


43. . . . 


2.84 


2.58 


2.32 


2.13 


1.04 


1.76 


1.61 


1.46 


1.33 


1.21 


44. . . . 


2.91 


2.64 


2.38 


2.18 


1.08 


1.81 


1.65 


1.5 


1.37 


1.23 


45. . . . 


2.97 


2.7 


2.43 


2.23 


2.03 


1.85 


1.69 


1.53 


1.4 


1.26 


48. . . . 


3.04 


2.76 


2.40 


2.28 


2.07 


1.80 


1.73 


1.57 


1.43 


1.20 


47. . . . 


3.1 


2.82 


2.54 


2.33 


2.12 


1.03 


1.76 


1.6 


1.46 


1.32 


48. . . . 


3.17 


2.88 


2.50 


2.38 


2.16 


1.07 


1.8 


1.63 


1.49 


1.34 


49. . . . 

PA 


3.23 


2.04 


2.65 


2.43 


2.21 


2.01 


1.84 


1.67 


1.62 


1.37 


50. . . . 


3.3 


3. 


2.7 


2.47 


2.25 


2.05 


1.87 


1.7 


1.55 


1.4 


52. . . . 


3.43 


3.12 


2.81 


2.57 


2.34 


2.13 


1.95 


1.77 


1.61 


1.46 




{ 



126 



ELECTROMAGNETS. 



Table IV«« 



MAn^mv Space occapled bjr DoaMa d 
Covered ^^ire**^ Continued. 



Wire numbersp B. and S. Gauge. 



Turns or 






















layers. 


















1 




15 


16 


17 


18 


10 


20 


21 


22 


23 


24 


54. . . . 


3.56 


3.24 


2.92 


2.67 


2.43 


2.22 


2.03 


1.84 


1.67 


1.51 


50. . . . 


3.7 


3 .36 


3.03 


2.77 


2.52 


2.3 


2.1 


1.9 


1.74 


1.57 


58. . . . 


3.83 


3.48 


3.13 


2.87 


2.61 


2.38 


2.18 


1.97 


1.8 


1.63 


60. . . . 


8.06 


3.6 


3.24 


2.97 


2.7 


2.46 


2.25 


2.04 


1.86 


1.68 


62. . . . 


4.00 


3.72 


3.35 


3.07 


2.79 


2.54 


2.33 


2.11 


1.92 


1.74 


64. . . . 


4.23 


3.84 


3.46 


3.17 


2.88 


2.63 


2.4 


2.18 


1.00 


1.79 


66. . . . 


4.36 


3.96 


3.57 


3.27 


2.07 


2.71 


2.48 


2.25 


2.05 


1.85 


68. . . . 


4.49 


4.08 


3.67 


3.37 


3.06 


2.79 


2.55 


2.31 


2.11 


1.01 


70. . . . 


4.62 


4.2 


3.78 


3.47 


3.15 


2.87 


2.63 


2.38 


2.17 


1.96 


72 ... . 


4.75 


4.32 


3.89 


3.57 


3.24 


2.95 


2.7 


2.45 


2.23 


2.02 



Turns or 
layers. 



74 
76 
78 
80 
82 

84 
86 
88 
90 
92 

94 

96 

98 

100 

102 

104 
106 
108 
110 
112 

114 
116 
118 
120 
122 



Wire Numbers, B. & S. Gauge: 



17 



4 
4 
4 
4 
4 

4 

4 
4 



11 
21 
32 
43 

54 
65 
75 



18 



3,67 
3.76 
3.86 
3.96 
4.06 

4.16 
4.26 
4.36 
4.46 
4.56 

4.66 
4.75 



19 



3.33 

3.42 

3.51 

3.6 

3.69 



.78 
.87 
.96 
.05 
.14 



4.23 

4.32 

4.41 

4.5 

4.59 

4.68 



20 



3.04 

3.13 

3.2 

3.28 

3.36 

3.45 
3.53 
3.61 
3.69 
3.77 

3.86 

3.94 

4.02 

4.1 

4.18 

4.27 
4.35 
4.43 
4.51 
4.59 



21 



2.78 

2.85 

2.93 

3. 

3.08 

3.15 

3.23 

3.3 

3.38 

3.45 

3.53 

3.6 

3.68 

3.75 

3.83 



3.9 

3.98 
05 
13 
2 



4.28 
4.35 
4.43 
4.5 



22 



2.52 
2.59 
2.65 
2.72 
2.79 

2.86 
2 93 
2.99 
3.06 
3.13 

3.2 

3.27 

3.33 

3.4 

3.47 

3.54 
3.61 
3.67 
3.74 
3.81 

3.88 
3.05 
4.01 
4.08 
4.15 



23 



2.3 

2.36 

2.42 

2.48 

2.54 

2.61 
2.67 
2.73 
2.79 
2.86 

2.92 

2.98 

3.04 

3.1 

3.16 

3.23 
3.29 
8.35 
3.41 
3.47 

3.54 

3.6 

3.66 

3.72 

3.78 



24 



2.07 
2.13 
2.10 
2.24 
2.3 

2.35 
2.41 
2.47 
2.52 
2.58 

2.63 

2.60 

2.75 

2.8 

2.86 

2.91 
2.97 
3.03 
3.08 
3.14 

3.19 
3.25 
3.31 
3.36 
3.42 



^ 



WINDING OP ELECTROMAGNETS. 127 



Altera»tini^C«iTent Slectrovaffmct*. 



^The cores of etectromaf^nets to be used with alternating currents must 
> tatmiDAtedf and the laminations must run at right angles to the direc- 
n in which eddy currents would be set up. Eddy currents tend to cir- 
jeulate parallel to the coils of the wire, and tne laminations must, therefore, 
m longitudinal to or parallel with the axis of the cores. 
! The ootla of an alternating-current electromagnet off^* more resistance 
to the passage of the alternating current than the mere resistance of the 
eooductor in ohms. ' This extra resistance is called inditetance, and this 
eomluaed with the resistance of the conductor in ohms produces the quality 
criled imp edance. (See Index for Impedance, etc.) 

If L -B coefficient of self-induction, 
N -" cycles per second, 
R •■ re sistance, 

Impedance - V^a -f 4 irW'L^; 




MaTimum current •— 
Mean current » 



Maximum E.M.F. 

■ ■ ■ « 

Impedance 

Mean E.M.F. 
Impedance. 



I 



B[e*tliiflr •f TUKwktem^t Cell*. 

Profbbsor Forbes. 

/ «B current permissible. 

r( -■ resistance of coil at permissible temperature. 
PoToiBsible temperature » cold r X 1.2. 

t * rise in temperature C**. 

« -> sq. cms. surface of coil exposed to air. 



-v/^ 



.0 003 XtX9 
.24 X rj 



Oiarles R. Uoderhill gives the following formula as having been found 
by practise ^e moet accurate and complete for the design of plunger electro- 
Let P -> pull in pounds. 

B -> flux density in the working air-gap. 
I ■- length of the air-gap. 
IW — ampere-turns in the winding. 
A — cross section of plunger in sq. in. 
P» » pull at 10,000 ampere-turns and 1 sq. in. of plunger, 
n "■ ampere-turn factor. 
L " length of the winding in inches. 

Then, the pull due to an iron-clad solenoid is 

APe (/AT - n) 



P - 



10,000 - n 



and, at points along the uniform range of solenoids, the pull for the plunger 
dcctromBgnet willbe 



p . X ( ^^ + ^^^-— ^-^Y 

^ ^ V 7.075,600 P ^ 10.000 - n / 



Here I must include the extra length assumed due to the reluctance outside 
of the worldng air-gap. 



128 



ELECTROMAGNETS. 



!■ P««Bds, 



Aaiper«-tan Factor mt 



L 


P. 


n 


1 


33.0 


3600 


2 


28.3 


3160 


3 


23.4 


2800 


4 


19.2 


2500 


6 


16.0 


2200 


6 


13.8 


1970 


7 


12.2 


1760 


8 


11.0 


1580 


9 


10.0 


1400 


10 


9.2 


1230 


11 


8.4 


1100 


12 


7.8 


1060 


13 


7.2 


840 


14 


6.8 


725 


15 


6.4 


625 


16 


6.0 


526 


17 


6.7 


430 


18 


6.3 


850 


19 


6.0 


270 


20 


4.7 


210 



To approximate the curve of a plunser electromagnet at points bflhfi 

le center of the winding, and the end of the wincunc where the phflj 

enters, assume that the curve is a straight line for the last .4 of the i 



tance: then the pull at any point, la as measured in inches, back from t 
end ot the winding, will be 



{t. 



IN^ 



laP^ilN -n) 



076,600 «» ' .4 L (10,000 



-n)) 



where L equals length of the winding. In this it is assumed that the wind 
is approximately as long as the inside of the frame. 

In cases where a low density in the core is used, the curve for the in 
clad solenoid effect cannot be calculated with so high a degree of aoenn 




.// ////f/////ff £f^^////{{£f/A 



7//////////////M////^//^ 



r'f!^^:^^^::^^.^^T:y^.-T 




zvu.'m^iimiLLM 



FiOB. 2, 3, 4 and 5. Shapes of Electromagnets. 



1 

WINDING OF ELECTBOMAGNBTS. 129 



i 



POSITIONS INSIOS OF WIHDINe,(INCHES} 
no. fl. OhuKotarlttliM ot El«ctri>m*fD*t*, 



130 



BLECTBOICAQNBTS. 



^ 

^ 



) 



Fig. 3 shows a simple ooll and planger and Fig. 4 the same magnet, but 
with an iron jacket or return curoaii about the outside of the winding. 
This is usually referred to as an iron-olad solenoid. 

Bv placing a ** stop " inside the winding at the rear end of the frame 
we hare the plunger electromagnet in Fig. 8. 

It is to be obserred that the same coil and the same plunger are used in 
each case. The cross section, A^ of the plunger is just 1 square inch. 

Beferring to Fig. 8, curve "a" is due to the simple coil and plunger in 
Fig. 2, and cunre ** 6 " is due to the iron-clad solenoid in Fig. 4. the ampere- 
turns in the winding being 10,000 in all eases. It will be noticed that the 
oiilv difference between curves ** a" and " fr " is that curve " 6 " is slightly 
hiffher at distances greater than 6 in., owing to the confinement or the 
field, and also that it bends upwiutl for short distances instead of falling 
oif like curve " a.** This latter effect is due to the attraction between 
the end of the plunger and the iron frame of the iron-olad solenoid. How- 
ever, the pull throughout the eenter of the winding is the same in both 
oases. 

Where there is » hifl^ density of the lines of force in the plunger, aa 
additional reluctance is in evidence, which 
must be added to the length of the work- 
ing air-gap. 

The range of a solenoid is the distance 
through wEich its plunger will perform 
work when the wmding is ene(gised« 
llie greater the length of the solenoid, 
the greater will be the range, as the range 
varies in nearly direct proportion witn 
the length of the solenoid. The range of 
the solenoid is constant regardless of the 
ampere-turns, but Uie attraoti<m or pull 
on the plunger varies directly with the 
amxiere-tums after the core is saturated, 
there being some variation below this 
point due to change in the permeability 
of the plunger. 

In designing a solenoid, the pull should 
be taken at a point on the curve which 
is considerably below the maximum, as 
this will allow for enough extra attraction 
to overcome any friction, and also to keep 
assuming a low point for the necessary pull, 
greatly moreaseo. 




AMWIW-TUIM* 



Fio. 7. PuU due to Solencrfda of 
Different Loigths with Plunger 
1 sq. in. in Cross-Section. 



the load moving, and by 
the effective range will be 



^ 



PROPERTIES OF WIRES AND CABLES. 

RBTiaao BT Habold Pindbr, Ph.D. 

Tax unit of resbtanoe now universally uaed ia the International Ohm. 
Tbe following multiples of this unit are sometimes employed. 

Megohm — 1,000.000 ohms, 
lliorohm « 0.000,001 ohm. 

The following table gives the value of the principal praotioal units of reeis- 
taaee which existed pzevioai to the establishment of the International Units. 




( 



Unit. 



International ohm . . 

B, A. ohm 

ohm 

I's ohm ... 



International 
Ohm. 



1. 

0.0866 
0.9072 
0.9407 



B.A. 
Ohm. 



1.0136 
1. 

1.0107 
0.0536 



Legal Ohm 

1884. 



1.0028 
0.0804 
1. 
0.9434 



Siemens's 
Ohm. 



1.0630 

1.0600 
1. 



Ihtis to reduce British Association ohms to international ohms we divide 
bv 1.0136. or multiply by 0.9866; and to reduce legal ohms to international 
ohms we divide by 1.0028, or multiply by 0.9972, etc. 



Lei 



I 
A 
R 



Sp«clllc ]|«alateMC«. 

length of the conductor, 
cross section of the conductor, 
resistance of the conductor, 
specific resistance of the conductor. 



Then 



or 



R 



I 

'a* 



If I is meafured In eentimeten and A in square oentlmeterB, p Is the 
resistanoe of a centimeter cube of the oondnctor. If Ms measured in 
iaehes and A in square inches, p is the resistance of an inch cube of the 
eondoctor. 

In tei^raph and telephone practice, speoiflo resistance Is sometimes 
expressed as the weight per mi/e-oAm, wnicn is the weight In pounds of a 
Mudiietor one mile long naving a resistance of one ohm. 

Another oommon way of expressing speoiiic resistance Is in terms of 
sAsif per milrfooi, i.e., the resiatance of a round wire one foot long and 
QuQOi inch In mameter ; I is thenmeasured in feet and A in circular mils. 

Xierohma per inch cube ■• 0.3887 X microhms per centimeter cube. 

Ponnds per mile>ohm ■- 67.07 X microhms per centimeter cube X 

speoiflo gravity. 

Ohms per mil-foot » 6.016 X mlcrohma per cantimeter cube. 

181 



132 



PROPERTIES OP CONDUCTORS. 



ftpecMIc CoMdMCtiTftj U the reciprocal of speoifio renstanoe. It e ^ 
vpeofio oonductivity 

I 

^' RA' 

1 

c — -■ 

P 

By RelatiTC ^r P«rceBtoc« CoMdnctlTltT' of a aample is meant 
100 times the ratio of the conductivity of the sample at standard tant- 
perature to the oonduotivity of a conductor of the same dimensions niade 
of the standard material and at standard temperature. If Ao ib the specific 
resistance of the sample at standard temperature and a* is the specific resist- 
ance of the standard at standard tempw ature, then 

Percentage conductivity — 100 — 

Po 
In comparing different materials, the specific resistanee should always 
be determined at the standard temperature, which is usually taken aa 0" 
Centigrade. If it is inconvenient to measure the resistance of the sample 
at the standard temx>erature, this may be readily calculated if the tem- 
perature coefficient a of the sample is known, i.e., 

l + o/ 
where pt ifl the specific resistance at temperature t. 

]lffattlile«ieni*a Staadard of CoBdnctlvltj', which is the commercial 
standard, is a copper wire having the following properties at the standard 
temperature of Or C. 

~ " 8.89. 

1 meter. 

1 gram. 

.141729 ohms. 

1.594 microhms per cubic centimeter. 

100%. . 



Specific gravity 

Length 

Weight 

Resistance 

Specific Resistance 

Relative Conductivity 



SpecUlc lteiiiiit»nc«. Relative RcMifaiteiic^, aad llelatlT« 

Coadactl«'ity of Coadactom. 

Referred to Matthiessen's Standard. 





Resistanee in Microhms 








at 0' 


»C. 


Relative 


Relative 


Metals: 






Resis- 
tance. 
% 


Conduc- 


Centimeter 
Cube. 


Inch Cube. 


tivity. 
% 


Silver, annealed . . . 


1.47 


.679 


92.5 


108.2 


Copper " 


1.65 


.610 


97.6 


102.6 


Copper (Matthiessen's 

Standard). 


1.594 


.6276 


100 


100.0 










Gold (99.9% pure) 


2.20 


.865 


138 


72.6 


Ahimfniim (00% pnrft^ 


2.56 


1.01 


161 


62.1 


Zinc 


5.75 


2.26 


362 


27.6 


Platinum, annealed . . . 


8.98 


3.63 


665 


17.7 


Iron 


9.07 


3.67 


670 


17.6 


Nickel 


12.3 


4.86 


778 


12. g 


Tin 


13.1 


6.16 


828 


12.1 


Lead 


20.4 


8.04 


1.280 


7.82 


Antimony 


35.2 


13.9 


2.210 


4.53 


Mercury 

Bismutn 


94.3 


37.1 


5,930 


1.69 


130. 


61.2 


8.220 


1.22 


Carbon (graphitic) . . 
Carbon (arc light) . . 


2.400-42,000 


950-16.700 






about 4.000 


about 1,590 






Selenium 


6X10" 


2.38 X10« 







GENERAL. 



133. 



LdquidB»t 18<*C. 


Ohms per Genti- 
motor Cube. 


Ohmii per Inch 
Cube. 


Pnreimtcr 


2650 

30 
4.86 
1.37 
9.18 
1.29 

21.4 


in.'tn 


Sea water 


11 R 


Sulphmie acid, 5% 

Snlpharie acid, 30% 

Solphiiric add. 80% 

Nitricadd, 30% 

Zine solphate. 24% 


1.93 
.544 

3.64 
.512 

8.54 



VeatperAinr* C^eflident. 



Tlie 
doetor. 

Let 



reaistanoe of a conductor varies with Xhe temperature of the 



con* 



( 



Ro " Reeietance at 0**. 
R <- Resistance at (^. 
R - iWl + a 0. 

a is called tlie feinpemter« coefficient of the oonduotor. 100 a is the per- 
eeatage change In resistance per d^ree change in temueratore. 

The following ralues of the temperature coefficient naye been found for 
temperatures measured in dozrees Centigrade and in degn^ees Fahrenheit. 
It is to be noted that the coomoients yary considerably with the purity of 
th» conductor. 



Pure Metals. 


Centigrade 


Falirenhdt 

a 


Slyer, azmealed 

Corner, annealed .... 

G«WC».9%) 

Ahuninium (99%) .... 
SSm 

^iDam, annealed . . . 

IPOO 

Nkkfli 


0.00400 

0.00428 

0.00377 

0.00423 

0.00406 

0.00247 

0.00625 

0.0062 

0.00440 

0.00411 

0.00389 

0.00072 

0.00354 


0.00222 
0.00242 
0.00210 
0.00236 
0.00226 
0.00137 
0.00347 
0.00346 


Tin . ; 


0.00245 


Lesd 

^imony 

Biansth 


0.00228 
0.00216 
0.00044 
0.00197 



Matthieseen's formula for soft copper wire 

R - Bo (1 + .00387* + .00000697^). 

TIm wire used by Matthiessen.was as pure as could be obtained at the 
tine (1^0), but in reality contained considerable impurities; the above 
fecmnk, therefore, is not generallv applicable. Later experiments have 
ihown that for all practical work the above equation for copper wire may 
bsvritten . . «^ 

H - «b (1 + .00420 for « in • C. 



PROPERTIES OF CONDUCTORS, 



111 

III 



,ST1.S« 


iU : § 1 : S 


■iCiu«iD »gT»<lB 


« o« : S S jr. 


■tpoi annbg «! 






S S?! : : : : : 


*a ■loTM »Diir»n 


S i§ i ; ; : : 


HMJ3III low J»J 


MM ; ; M 


prfs^sas'H 


IE. 4 

17.4 

20,0 
27.8 

76.6 


qooiMdralvSoiM 


s S3 2 a a s s 


InnioiOTWOJIW 


S !£8 S = S 3 . 







J ELECTRICAL PROPERTIEa OF METALS. 135 



^.^^oJJS^ 


s 8Si s ; g ; ;§ 1 


s ;; ! 




■«)U«D ■>BF«»B 


^ ™8 . ; , : iS s. ; ; ; 




mill ! H 




■mH°^P^ 


i=i; :! ; : 1 ilM; 


-»a ■»««'d »«mi»H 


S i^ : i i ; ii 11 ; M 


ssrSlj 


i ;^5 i ; ; ;3 P i ; : S 


;a':,-sia. 




„^»S%, 


. ;:«s Is s s «! s§g§: S 




« *-» - « ^ ^ 


"■niMOHI ■£>*»■. 


.. . = s= s . ,» sss=s s 

S 2|2 — ^ p -- »" - 




■ 

1 


jlr 

Ml 

k-Ji 

tills 
if 





PBOPERTI£S OF CONDUCrOR8. 



■Al[&«jQ igndg 



Bpnnoj 'n»«CMj]g 






■DoOW»an(0'«>» 



!i ;M M ; Mil i : 
IsTTiTTTiieTT 



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«3 $!!3 « Si : . 






is 

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r 

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Si 



PHYSICAL AND ELECTRICAL PROPERTIES OP METALB. 137 

pmmi -ipoi SSI ■ i«==i S' 5 S S 

iiqnO I JO tqlHjU ... '. ". .^.^,°. ^ ". ". " 



ipanoj 'qilmjig 



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S s i S s =1 il== E^= 2 




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PHYSICAL AND ELECTRICAL PROPEBTIEB OF IfETAU. 139 



■•a ■iDioj >iiiit>n 
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140 



PROPERTIES OF CONDUCTORS. 






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3 d d SQQfdaQ d d 



WIRE GAUGES. 



141 



The naes of wir«s are ordinarily expressed by an arbitrary aeries of num- 
Unfdrtunately there are several independent numbering methodB, 
■0 that it » alwajrs necesaary to specify the method or wire gauge U8«l. 
The following table gives the numbers and diameters in decimal parts of an 
inch tar the various wire gauges used in this country and England. 

Pttrta •# 



Number 
of 

Wire 
Onto. 


Roebling or 

Washburn 

AMoens. 


Brown A 
Sharpe. 


Birming- 
ham, or 
Stubs. 


English 

LegaTStand- 

ard. 


Old English* 
or London. 


ft^> 


.400 


• • V ■ • • 


• • ■ ■ 


.464 




5H> 


.430 


• ••■•■ 


• • a • 


.432 


• ••••• 


4-0 


.393 


.4600 


.454 


.400 


.4540 


^ 


.362 


.4096 


.425 


.372 


.4250 


a^ 


.331 


.3648 


.380 


.348 


.3800 





.307 


.3249 


.340 


.824 


.3400 


1 


.283 


.2893 


.300 


.300 


.3000 


2 


.263 


.2576 


.284 


.276 


.2840 


8 


.244 


.2294 


.259 


.253 


.2590 


4 


.225 


.2043 


.238 


.232 


.2380 


5 


.207 


.1819 


.220 


.212 


.2200 


6 


.192 


.1620 


.203 


.192 


.2030 


7 


.177 


.1443 


.180 


.176 


.1800 


8 


.162 


.1285 


.165 


.160 


.1660 


9 


.148 


.1144 


.148 


.144 


.1480 


10 


.135 


.1019 


.134 


.128 


.1340 


U 


.120 


.09074 


.120 


.116 


.1200 


12 


.105 


.08081 


.109 


.104 


.1090 


13 


.092 


.07196 


.095 


.092 


.0950 


14 


.080 


.06408 


.083 


.080 


.0830 


15 


.072 


.05706 


.072 


.072 


.0720 


10 


.063 


.05082 


.065 


.064 


.0650 


17 


.054 


.04525 


.058 


.056 


.0580 


18 


.047 


.04030 


.049 


.048 


.0490 


19 


.041 


.08589 


.042 


.040 


.0400 


20 


.035 


.03196 


.035 


.036 


.0350 


21 


.032 


.02846 


.032 


.032 


.0315 


22 


.028 


.02534 


.028 


'.028 


.0295 


23 


.025 


.02257 


.025 


.024 


.0270 


24 


.023 


.02010 


.022 


.022 


.0250 


25 


.020 


.01790 


.020 


.020 


.0230 


36 


.018 


.01594 


.018 


.018 


.0205 


27 


.017 


.01419 


.016 


.0164 


.01875 


28 


.016 


.01264 


.014 


.0148 


.01650 


29 


.015 


.01125 


.013 


.0136 


.01550 


30 


.014 


.01002 


.012 


.0124 


.01375 


31 


.0135 


.00893 


.010 


.0116 


.01225 


32 


.0130 


.00795 


.009 


.0108 


.01125 


33 


.0110 


.00708 


.008 


.0100 


.01025 


34 


.0100 


.00630 


.007 


.0092 


.0095 


35 


.0095 


.00561 


.005 


.0084 


.0090 


38 


.0090 


.00500 


.004 


.0076 


.0075 


37 


.0085 


.00445 


• • • • 


.0068 


.0065 


38 


.0080 


.00397 


• ■ • • 


.0060 


.0057 


39 


.0075 


.00353 


• ■ • • 


.0052 


.0050 


40 


.0070 


.00314 


• • • • 


.0048 


.0045 



( 



142 



PROPERTIES OP CONDUCTORS. 



_ »• — Used almost universally in this oountry for iron 
and steel wire. 

BrawM * BUaurpm €taMic«« — The American standard for wires for 
eleotrical purposes. 

BlnsBliBrliMM ChaoM. — Used largely in England and also in this 
country for wires other than those made especially for eleotrical purposes, 
ezoepting iron wire. 



Saw of the Sro 



) 



The diameters of wires on the B. and S. gauoe are obtained from the 
geometrio series in which No. 0000 — 0.4600 inch and No, 36 — .005 in., 
the nearest fourth significant figure being retained in the areas and diametera 
so deduced. 



Let 
llien 



n — 
d- 



gauge number (0000 -• - 3; 000 — - 2; 00 — — 1). 

diameter of wire in inohes. 
0.3249 

1.128* * 



Wires larger than No. 0000 B. and S. are seldom made solid but are 
built up of a number of small wires into a strand. The group of wires is 
called a "strand:" the term "wire" being reserved for the individual wires 
of the strand. Strands are usually built up of wires of such a siie that the 
cross section of the metal in the strand is the same as the cross section of a 
soUd wire having the same gaug^ number. 

If n — number of concentric layers around one central strandi 



then 



3 (n* + n) + 1 *. t metal area 

(2n+l)a " ™**° *" available 



The number of wires that will strand will be 8 n (n + 1) + !• 



Number of Strands. 


metal area 
available area 


1 
7 
19 
37 
61 
91 


1.000 
.778 
.760 
.755 
.753 
.752 



•lietttlilBflr Cor«. — The number, N, of sheathing wires 
eter, d, which will cover a core having a diameter. D, is 



having a diam- 






COPP£B WIRE TABLES 



143 



of C«Bi 



■••■clal Wlr«. — Aremc* 



FwCcntConduetrnty (Matthieaaen's Standard 100) 

Speoifie GraTity 

Pbuadfl in 1 cubic foot 

IVMiiidi in 1 cubic inch 

Pbunds per mile per careular mil 

Ultimate Strength 



eq. m. 

lb. X in. 
Modnius of Elasticity 



in. X sq. in. 
Cbefficient of Linear Expansion per •C 

Cbeffident of Linear Expannon per * F. 

Mdtins Point in*C .,.,. 

luting P6int in * F. .* 

Spedfie Heat (wafct-«eoonda to heat 1 lb. 1** C.) . . 

IbsoMl Conductivity (watte through cu. in., tem- 
perature gradient 1** C.) 



IGoohme per centimeter cube 0^ C 

IGaohmfl per inch cube 0^ C. . . 

Ofams per nul-foot 0^ 

Ohms per mil-foot 20^ C 

Rerifltanoe per mile O' C 

Bcsistanoe per mile 20^ C. . 

^nods per mile ohm 0^ C. . 

Pounds per mile ohm 20*' C. . 
Tompvature Coefficient per ** C. 
T«nperature Coefficient per ^ F. 



• • • • 



• •••••• 



Annealed. 



100 

8.9 

555 

.321 

.0160 

23.000 

• ••••«•• 

.0000171 

.0000095 

1060 

1920 

176 

8.7 

1.594 

.6276 

9.59 

10.36 

50.600 

cir. mils. 

54.600 

cir. mils. 

810 

875 

.0042 

.00233 



Hard. 



98 

8.94 

558 

.323 

.0161 

55,000 

16,000.000 
.0000171 
.0000095 

1060 

1920 

176 

8.7 

1.626 

.6401 

9.78 

10.67 

51.600 

cir. mils. 

55,700 

cir. mils. 

830 

896 

.0042 

.00233 



( 



144 



PROPERTIES OF CONDUCTORS. 



•peclllc ^wwtltlM of Varlew 



•f C:«pper wtOi 



SubstanoQB alloyed with Pure Copper. 



Carbon: 

Copper with 

Sulphur: 
Copper, with 

PhoephoniB: 
Copper, with 
Copper, with 
Copper, with 

Araenio: 
Copper, with 
Copper, with 
Copper, with 

Zinc: 
Copper, with 
Copper, with 
Copper, with 

Iron: 
Copper, with 
Copper, with 



.05 per cent of carbon . . 

. 18 per cent of sulphur . . 

. IS per cent of phosphonia 
.96 per cent of phosphonu 
2.6 per cent of phoephoruB 



traces of arsenic .... 
2.8 per cent of arsenic . . 
6.4 per cent of arsenic . . 



traces of line 

1 .6 per cent of sine . . 
3.2 per cent of sine . . 

.48 per cent of iron . . 
1 .06 per cent of iron . . 



1 .33 per cent of tin . 
2.52 per cent of tin . 
4.9 per cent of tin . . 



Tin: 
Copper, with 
Copper, with 
Copper, with 

Silver: 

Copper, with 
Copper, with 

Gold: 

Copper, with 3.5 per cent of gold . . 



1 . 22 per cent of silver 
2.45 per cent of silver 



Aluminum: 
Copper, with 



Conducting 

Power of 

Hard -drawn 

AUoy. Pure 

Soft Copper 

being 100. 



. 10 per cent of aluminum 



77.87 

92.06 

70.34 

24.16 

7.62 

60.08 

13.66 

6.42 

88.41 
79.37 
69.23 

35.92 
28.01 

60.44 
33.93 
20.24 

90.34 
82.52 

67.94 

12.68 



Temperature 
Centigrade. 



18.3 

19.4 

20.0 
22.1 
17.5 

19.7 
19.3 
16.8 

19.0 
16.8 
10.3 

11.2 
13.1 

16.8 
17.1 
14.4 

20.7 
19.7 

18.1 

14.0 



COPPER WIRE TABLES. 145 



Below are ^ven the Oopper Wire Tables of the American Institute of 
Beetricsl fiigmeers. The table for the Brown and Sharpe sauce is derived 
from the following fonnulas: 

Lei A — wire gauge number. 

d "■ diamet,er of wire in inches. 
C.1C ■" area in dreular mils. 

r — reeiatanoe in ohms per 1000 feet at 20* G. 
m — weight in pounds per 1000 feet. 
0.3240 



Vm d — 

CM. ^ 



1.123" 
105.500 



B 



1.261* 
r - 0.09811 X 1.261* 

810.5 
• " 1.261* 

A uKfoI approximate formula for resistance per 1000 feet at about 20* C. 
r - 0.1 X 2*. {^ - 1.26; 2t - 1.5o). 

Fnim this it is seen that an increase of 3 in the wire number corresponds 
to donbfing the resistance and halving the cross section and weight. Also, 
that aa increase of 10 in the wire number increases the resistance 10 times 
and diminiahes the oroes section and weight to ^th Uxeir original values. 

Tbe data in the following table has been computed as follows : Mat- 
thictsen'a standard resistivity, Matthiessen's temperature coe£Bcient, specific 
. fitvityof copper --S^. lusistanoe in terms <» the international ohm. 

MattUesien's standard 1' meter gramme of hard drawn copper— 0.1469 
B.A.U. a <P C. Ratio of resistivity hard to soft oopper 1 .0226. 

Matthiessen's standard 1 meter sramme of soft drawn copper— 0.14366 
BXU. @ OP C. One BJL.U. - OiMW international ohm. 

MtrthJiesBen's standard 1 meter gramme of soft drawn copper— 0.141729 
iatenational ohm at HP G. 

Ttmperature coefBcients of resistance for 20^ 0., 60^ G., and W* G., 1.07968. 
1J«5 and 1.33681 respectively. 1 foot -6.3048028 meter, 1 pound - 453.50266 
SnauBfli. 

Althongh the entries in the table are carried to the fourth significant 
j!«>t, the eompaUtions have been carried to at least five figures. The last 
jVkii therefore correct to within half a unit, representingan arithmetical 
^cp«e of aceuracv of at least one part in two thousand. The diameters of 
»«B.» 8. or A. W. G. wires are obtained from the geometrical series in 
vbiek No. 0000=0.4600 Inch and No. 36 = 0.006 inch, the nearest fourth sig- 
Bileaat digit being retained in the areas and diameters so reduced. 

It a to he observed that while Matthiessen's standard of resistivity may 
Be panoanently reoogniaed, the temperature coefficient of its variation 
vbkh he Introduoed, and which is here used, may in future undergo slight 

ItllliML 



( 



n 



146 



PB0PBBTIB8 OF CONDUCTOB8. 



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COPPER WIRE TABLES. 



147 



m 
m 

95 
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148 



PBOPEBTIE8 OF 0ONDUCTOB8. 




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COPPER WIRE TABUBB. 



140 



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PROPEBTIES OF CONDUCTOB8. 



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COPPER WIRE TABLES. 



151 



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U%ii ^ss«s ssssKs 









otiqi-ic« ao«iqo»3 S-^aS^o 

SMII tsijiis it§s^« »*«'*' 



• r • m 9 






MCtvHf^fN *4 



§1=21 



»^'*'^'i •^t'^? ???^S^ §883^8 

sens ss§s« »^«^«« *»--"* 






ACVCVvi^i^ «-« 



S-^S^S S8<StS3 ^co(i^r»« ^««o 

ssssa sjssji^si ^SSli §§!§! 









_• • • • ♦ 



SSo! 



• » • » • • • ^ ^ ^» 
e«i^ooo ooooo 






So 



ooodd 



IS! 



oooeo 



- ■ • • • 
01 •» 



i 



• • • • • * A 



ei»«-ieoe 



oooo< 



§81 

ss: 

• • ■ ■ « 

ooooo 



OOOOO 



il 



5g sS|i§ |i§S 
91 ot-iBQeo S^c^^ 



ooooo 



ooooo 
ooooo 



• • ■ - - 

ooooo 



:888i 

_w • • • - 

ooooo 



9SS! 



odddo 



e?i 



ilii 



poooo 



mil 



04 






000{i-4C4iq iHOt^iHi^ @^3S^ 

Uiu iMi^ «^s8«ss 



§8§i§ Sisss nui 



Sills 



loqoo 

[S8;J8 



oeoo . 

• • • • * 



ne^r^Mv^ 



S8SI§ §! 



'8 898S8 



ooooo ooooo ooooo 



ooooo 

a • • • ■ 

ooooo 



ooooo 

» • • • • 

ooooo 



ooooo 



8s sssss s;ss8s aasiss s^sss^ ssss^^^ 



1 



t«e9S9 r*! 



oomSS 
&o«»dao 



• • • • • • • • ■ • • 



f •IB r**5 



a»^«^ dvsooo ooodo 



^^T< 



odo< 



01 






( 



Il 



111 



FBOFBltTlES OF CONDUCTORS. 



I 



It! 

Ill t 



COPPER WIRE TABLES. Ibi 



Si §9Slii sSP^S SSiS^ 8«88« eeoA^ 

■5 sSsfifi nSs^s 885fis qZSSs Sfis«*5 

99 fiOOvO 000*^*^ *^99C9& 09C«wCl 2Q9^*0 

»e oeooo cSeooe oSeeo oooo<S SnSiiaS 



»eooe oeoeo eoeeo eoeeo oeo 



s; 



Crfi^noS eSv^Sio^o lo^oMO e»e9ion 
oo oeooo ooooo ooooo ooeoo ooooo 



bS s^ssS SSS9S S&ssa XH^ssfi s^ssssr? 

I 89 fi09**9 OxvvO vSO^fi^ O^es^^S trs^^'^t' 

SS SSfififi SSS9S SSS9S9 xSxSss S!*^S3SX 

33 **53^ SR^^o 9$«?99 o.S^^I *in*1"t^ 

I oo ooeeo ooooo ooooo odooo ooooo 



SS 8§2*** SS-4e«A o 

ll iiiSS ^^M% |25?5;? Scjcoc,-, «?^^«-. 

oo doodo oo-«^ «^SSSil SSggg ||?J| 



si lii^^ iiSSI ^Ssjjss ^s 

SS S55-« ».SS9^S «^:85^^ «o^oq«)^ "^^i^^^ 

oo oeooo oo^«rf »«SSa8 S8838 88SS8 

»H »-i 55 Z oS "I'^wi 



o^ iiiii i§|S^ %^^M s88oo «^^ 

I O© e€>dOG» od-.«« "ooo^gg ^8Sg| Sg§S8 

* • ^ 



'S= S5SSS &S$S8S3 882^298 ^888;; SS8$88 

f 



154 



PROPERTIES OP CONDUCTORS. 



The following oondenBed copper wire tables for both solid and stranded 
conductors are more convenient tor ordinary calctilations. 

Aolld Copper ITIre. 



No. 
B.A8. 


Diam. 
Mils. 


Area, 
ar. Mils. 


Weight. Pounds. 


Resistance. 20® C. 


Bare. 


1000'. 


Mile. 


Feet 

per 

Pound. 


1000*. 


Mile. 


0000 

000 

00 



1 

2 
3 
4 

5 
6 
7 
8 

9 
10 
11 
12 

13 
14 
15 
16 

17 
18 
19 
20 


460 
409.6 
364.8 
324.9 

289.3 
257.6 
229.4 
204.3 

181.9 
162.0 
144.3 
128.5 

114.4 
101.9 
90.74 
80.81 

71.96 
64.08 
57.07 
50.82 

45.26 
40.30 
35.89 
31.96 


211,600 
167,800 
133,100 
105,500 

83.690 
66.370 
52.630 
41,740 

33.100 
26.250 
20,820 
16,510 

13,090 

10.380 

8.234 

6,530 

5.178 
4.107 
3.257 
2,583 

2.048 
1.624 
1,288 
1,022 


640.5 
508 
402.8 
319.5 

253.3 
200.9 
159.3 
126.4 

100.2 
79.46 
63.02 
49.98 

39.63 
31.43 
24.93 
19.77 

15.68 
12.43 
9.858 
7.818 

6.200 
4.917 
3.899 
3.092 


8,381 
2,6^2 
2,127 
1,687 

1,337 

1,062 
841.1 
667.4 

529.0 
419.5 
332.7 
263.9 

209.2 
166.0 
131.6 
104.4 

82.79 
65.63 
52.05 
41.28 

32.74 
25.96 
20.59 
16.33 


1.561 
1.969 
2.482 
3.130 

3.947 
4.977 
6.276 
7.914 

9.980 
12.580 
15.87 
20.01 

25.23 
31.82 
40.12 
50.59 

63.79 
80.44 

101.4 

127.9 

161.3 
203.4 
256.5 
323.4 


.04893 
.06170 
.07780 
.09811 

.12370 
.1560 
.1967 
.2480 

.3128 
.3944 
.4973 
.6271 

.7908 
.9972 

1.257 

1.586 

2.000 
2.521 
3.179 
4.009 

5.055 
6.374 
8.038 
10.14 


.2583 
.3258 
.4108 
.6180 

.€631 

.8237 

1.0386 

1.3094 

1.0516 
2.0824 
2.6257 
3.3111 

4.1754 
5.2652 
6.6370 
8.374 

10.560 
13.311 
16.785 
21.168 

28.690 
33.655 
42.440 
53.540 



STRANDED COPPER WIRE. 



155 



No. 


Diam. 
Mils. 


Ar«a 


Weight PoundB. 


Reflistanee 20** G. 
68* F. 


B^8. 




Or. Mils. 












Bare. 


LOOO*. 


Per 
MUe. 


Feet 
per lb. 


1,000'. 


Bflle. 






1.500.000 


4.575 


24.156 


.219 


.006902 


.03644 






1.250.000 


3.813 


20.132 


.262 


.008282 


.04373 




1.152 


1.000.000 


3.050 


16.104 


.328 


.010353 


.05466 




1.125 


050.000 


2,808 


15,200 


.345 


.010900 


.05755 




1.002 


000.000 


2,745 


14.404 


.364 


.01150 


.06072 




1.062 


850.000 


2.503 


13.688 


.385 


.01218 


.06431 




1.036 


800,000 


2.440 


12.883 


.409 


.01294 


.06832 




090 


750.000 


2.288 


12.078 


.437 


.01380 


.07286 




963 


700.000 


2.135 


11,273 


.468 


.01479 


.07809 




027 


650.000 


1,083 


10.468 


.504 


.01593 


.08411 




801 


000.000 


1.830 


0.662 


.546 


.01725 


.09108 




855 


550.000 


1.678 


8.857 


.596 


.01882 


.09937 




810 


500.000 


1,525 


8,052 


.655 


.02070 


.10930 




770 


450.000 


1.373 


7,247 


.728 


.02300 


.12144 




728 


400.000 


1.220 


6.442 


.819 


.02588 


.13664 




670 


350.000 


1.068 


5.636 


.936 


.02958 


.15618 




630 


300.000 


015 


4.831 


1.003 


.03451 


.18221 




590 


250.000 


762 


4.026 


1.312 


• .04141 


.21864 


OOQO 


530 


211.600 


645 


3.405 


1.560 


.04893 


.2583 


ooo 


470 


167,800 


518 


2.700 


1.049 


.06170 


.3258 


00 


420 


133.100 


406 


2.144 


2.463 


.07780 


.4108 





375 


105^500 


322 


1.700 


3.106 


.09811 


.5180 


1 


330 


83.600 


255 


1,347 


3.941 


.12370 


.6531 


8 


201 


66.370 


203 


1,072 


4.926 


.15600 


.8237 


s 


261 


52.630 


160 


845 


6.250 


.19670 


1.0386 


4 


231 


41.740 


127 


671 


7.874 


.2480 


1.3094 



Tlw table ia oalculsted for untwisted strands; if the strand is twisted the 
erooi section of the copper at right angles to the length of the strand, the 
vciiht per unit length and the resistance per unit length will each increase 
&tn& 1 to 3 per cent, and the length per unit weight will decrease from 1 to 8 
per eent, depending on the number of twists per unit length and the number 
a vires in the stzmiid. 



( 



156 



PROPERTIES OF CONDUCTORS. 



Teaalle AtreBgtb of Copper Wlre« 

ROBBLINO. 



Numbera, 
B.ftS. 
Gauge. 


Breaking Weight, Lbs. 


Numbers. 
B.&8. 
Gauge. 


Breaking Weight. Lba. 


Hard- 
drawn. 


Annealed. 


Hard- 
drawn. 


Annealed. 


0000 

000 

00 



1 
2 
3 

4 

5 
6 

7 
8 


8.810 
6.580 
5.226 
4,558 

3.746 
3,127 
2.480 
1.967 

1.559 

1,237 

980 

778 


5,650 
4,480 
3.553 
2.818 

2.234 
1,772 
1,405 
1,114 

883 
700 
555 
440 


9 
10 
11 
12 

13 
14 
15 
16 

17 
18 
19 
20 


617 
489 
388 
307 

244 
193 
153 
133 

97 
77 
61 
48 


340 
277 
210 
174 

138 

100 

87 

60 

65 
43 
34 
27 



The strength of soft copper wire varies from 32.000 to 36,000 pounds per 
square inch, and of hard copper wire from 45,000 to 68,000 pounds per 
square inch, according to the degree of hardness. 

The above table is calculated for 34,000 pounds for soft wire and 60,000 
pounds for hard wire, except for some of the larger sises, where the breaking 
weight per square inch is taken at 50.000 poxmds for 0000, 000, aiMl 00, 
65.000 for 0, and 57,000 pounds for 1. 



n«HI.]»ni 



Copper 

ROEBLXNO 



Siie 


Resistance 


Breaking 


Weight 


Furnished 

in Coils 

as follows, 

HUes. 


Approx. Sise 
E.B.B. Iron Wire 
Equal to Copper. 


Dm Ob D. 

Gauge. 


in Ohms 
per Mile. 


Strength, 
Pounds. 


]^L 


9 


4.30 


625 


209 


1 


2 . 


10 


5.40 


525 


166 


1.2 


3 




11 


6.90 


420 


131 


.52 


4 




12 


8.70 


330 


104 


.65 


6 


Iron-Wire 


13 


10.90 


270 


83 


1.20 


64 


Qmagp, 


14 


13.70 


213 


66 


1.50 


8 




15 


17.40 


170 


52 


2.00 


9 




16 


22.10 


130 


41 


1.20 


10 ^ 



In handling this wire the sreatest care should be observed to avoid kinks, 
bends, scratches, or outs. Joints should be made only with Mclntire Con- 
nectors. 

On account of its conductivity being about five times that of E2x. B. B. 
Iron Wire, and its breaking strength over three times its weight per mile, 
copper may be used of wUon the section is smaller and the weight less than 
an equivalent iron wire, allowing a greater number of wires to be strung on 
the poles. 

Besides this advantage, the reduction of section materially decreases the 
electrostatic capacity, while its non-magnetic character lessens the self-induc- 
tion of the line, both of which features tend to increase the possible speed of 
signalling in telegraphing, and to eive greater clearness of enunciation over 
telephone lines, especially those of great length. 



WEIGHT OF COPPER WIRES. 



157 



ITelirlk* ^ C«9per Wire. 
Eiraunc Stbtbm, pbb 1,000 Fsbt and per Mils, in Pounds. 



Boglieh Legal 
Standard. 


Birmingham. 


Brown A Sharpe. 


« 




Weiffht. 


inBfils. 


Weight. 


Diameter 
in Mils. 


Weight. 


i 

7i 


1000 
Feet. 


MUe. 


1000 
Feet. 


Mile. 


1000 

Feet. 


Mile. 


6-0 


404 

432 

400 


052 
565 

484 


3,441 
2,983 
2.557 












fi-0 














4-0 


454 


624'" 


ai,294 


• • ■ • • 

460 


64i"* ■ 


3,'38i2"" 


W) 


372 


419 


2,212 


425 


547 


2,887 


410 


509 


2.687 


2^348 


367 


1,935 


380 


437 


2308 


365 


403 


2.129 


0324 


318 


1.678 


340 


350 


1,847 


325 


320 


1.688 


1 


300 


272 


1,438 


300 


272 


1,438 


289 


253 


1.335 


2 


270 


231 


1,217 


284 


244 


1,289 


268 


202 


1.064 


8 


252 


192 


1.015 


250 


203 


1,072 


229 


159 


838 


4 


232 


163 


800 


238 


171 


905 


204 


126 


666 


5 


212 


130 


718 


220 


146 


773 


182 


100 


529 


6 


102 


112 


589 


203 


125 


659 


162 


79 


419 


7 


178 


94 


496 


180 


98 


518 


144 


63 


331 


8100 


77 


409 


165 


82 


435 


128 


50 


262 





144 


63 


331 


148 


66 


350 


114 


30 


208 


10 


12S 


50 


262 


134 


54 


287 


102 


32 


166 


11 


116 


41 


215 


120 


44 


230 


01 


25 


132 


}?W>* 


33 


173 


100 


86 


100 


81 


20 


105 


13 


02 


25.6 


135 


96 


27.3 


144 


72 


15.7 


83 


14 


80 


19.4 


102 


83 


20.8 


110 


64 


12.4 


65 


15 


72 


15.7 


83 


72 


15.7 


83 


57 


9.8 


52 


16 


64 


12.4 


65 


65 


12.8 


68 


51 


7.9 


42 


17 


56 


9.5 


50 


58 


10.2 


54 


45 


6.1 


32 


18 


4S 


7.0 


36.8 


49 


7.3 


38.4 


40 


4.8 


25.6 


10 


40 


4.8 


25.6 


42 


5.3 


28.2 


36 


3.0 


20.7 


20 


38 


3.9 


20.7 


35 


3.7 


19.6 


32 


3.1 


16.4 


31 


32 


3.1 


16.4 


32 


3.1 


16.4 


28.5 


2.5 


13.0 


21 


33 


2.4 


12.5 


28 


2.4 


12.5 


25.3 


1.9 


10.2 


23 


24 


1.7 


9.2 


25 


1.9 


10.0 


22.6 


1.5 


8.2 


24 


22 


1.5 


7.7 


22 


1.5 


7.7 


20.1 


1.2 


6.5 


25 


30 


1.2 


6.4 


20 


1.2 


6.4 


17.9 


.97 


5.1 


2S 


18 


.98 


5.2 


18 


.98 


5.2 


15.9 


.77 


4.0 


27 


16.4 


.81 


4.3 


16 


.77 


4.1 


14.2 


.61 


3.2 


2S 


14.8 


.66 


3.5 


14 


.59 


3.1 


12.6 


.48 


2.5 


20 


13.6 


.66 


3.0 


13 


.51 


2.7 


11.3 


.39 


2.0 


30 
31 


12.4 


.47 


2.5 


12 


.44 


2.3 


10.0 


.30 


1.6 


11.6 


.41 


2.15 


10 


.30 


1.6 


8.9 


.24 


1.27 


32 


10.8 


.35 


1.86 


9 


.25 


1.3 


8.0 


.19 


1.02 


33 


10.0 


.30 


1.60 


8 


.19 


1.02 


7.1 


.15 


.81 


34 


0.2 


.26 


1.35 


7 


.15 


.78 


6.3 


.12 


.63 


35 


8.4 


.21 


1.13 


5 


'.075 


.40 


5.6 


.095 


.50 


36 


7.6 


.17 


.02 


4 


.048 


.256 


5.0 


.076 


.40 



i 



( 



The dJameten giren for the yarlons sizes are those to which the wire is 
Mtoally drawn. 



158 



PB0PERTIE8 OP CONDUCTORS. 



•f Copper Wli«« 

Mmsic Stbtbm — Per Kzlouetbr, in Kilooraiu. 



Number 
of Wire 
Gauge. 


Roebliog. 


Brown A 
Sharpe. 


Birmingham 
or Stubs. 


Legal 
Standard. 


e-0 


954.3 




• • • • 


970.9 


6-0 


833.9 


• « « • • 


• • • • • 


841.6 


4-0 


696.6 


954.3 


929.4 


721.6 


8-0 


691.0 


756.8 


814.6 


624.0 


:m) 


494.1 


600.2 


651.3 


646.2 





425.1 


480.4 


621.3 


473.4 


1 


361.2 


877.4 


405.8 


406.8 


2 


311.9 


^99.3 


363.3 


843.5 


8 


268.6 


237.4 


302.6 


286.3 


4 


228.3 


188.3 


256.3 


242.7 


5 


193.2 


149.3 


218.3 


202.7 


6 


166.2 


118.4 


185.9 


166.2 


7 


141.3 


93.9 


146.1 


139.7 


8 


118.3 


74.5 


122.8 


116.4 


9 


98.8 


69.0 


98.8 


93.6 


10 


82.2 


46.8 


81.0 


73.9 


11 


64.9 


37.1 


64.9 


60.7 


12 


49.9 


29.5 


63.6 


48.8 


13 


38.2 


23.4 


39.8 


38.2 


14 


28.9 


18.6 


31.1 


28.9 


15 


23.4 


14.7 


23.4 


23.4 


16 


17.9 


11.7 


19.1 


18.6 


17 


13.2 


9.23 


15.2 


14.1 


18 


9.96 


7.32 


10.8 


10.4 


19 


7.68 


6.80 


7.95 


7.22 


20 


6.52 


4.61 


6.52 


6.85 


21 


4.61 


3.65 


4.62 


4.61 


22 


3.54 


2.89 


3.64 


3.64 


23 


2.81 


2.16 


2.81 


2.59 


24 


2.38 


1.82 


2.19 


2.19 


25 


1.80 


1.44 


1.80 


1.80 


26 


1.46 


1.16 


1.46 


1.46 


27 


1.80 


.908 


1.16 


1.21 


28 


1.16 


. .720 


.884 


.988 


29 


1.02 


.672 


.762 


.833 


30 


.884 


.462 


.649 


.694 


81 


.822 


.359 


.461 


.607 


82 


.762 


.284 


.365 


.625 


88 


.644 


.226 


.289 


.461 


84 


.461 


.179 


.220 


.881 


86 


.406 


.141 


.113 


.819 


86 


.365 


.113 


.071 


.260 



STANDARD COPPEB STBANDS. 



159 



ROKBUNO. 



CJL 


Wiraa. 


Outride 
Diam. 


Weisht 
Ibfl.per 
lOOOft. 


No. 


Sise. 


2.000.000 
1,990.000 
1.900.000 


127 
127 
127 


.1255 
.1239 
.1223 


1.632 
1.611 
1.590 


6100 
5948 
5796 


135O.O0O 
IJKOfiOO 
1,7504)00 


127 
127 
127 


.1207 
.1191 
.1174 


1.560 
1.548 
1.526 


5643 
5490 
5338 


1.700.000 
MGO.00O 
1.600.000 


01 
91 
91 


.1867 
.1347 
.1326 


1.504 
1.482 
1.450 


5185 
5083 
4880 


1.650,000 
1.500,000 
1.450,000 


91 
91 
91 


.1305 
.1284 
.1262 


1.436 
1.412 
1.388 


4728 
4575 
4423 


1.400,000 
1350.000 
1.300.00O 


91 
91 
91 


.1240 
.1218 
.1196 


1.364 
1.340 
1.315 


4270 
4118 
3965 


l;2SD,U0O 
1.200,000 
1.150.000 


01 
61 
61 


.1178 
.1403 
.1878 


1.289 
1.263 
1.236 


3818 
3660 
3508 


I.IOOXXX) 
14UOJ00O 
1.000,000 


61 
61 
61 


.1343 
.1312 
.1280 


1.209 
1.181 
1.152 


3355 
3203 
3050 


950.000 
9Q04M)0 
860,000 


61 
61 
61 . 


.1247 
.1214 
.1180 


1.122 
1.093 
1.062 


2898 
2745 
2593 


800.000 
750,000 
7004)00 


61 
61 
61 


.1145 
.1108 
.1071 


1.031 
.997 
.964 


2440 
2288 
2135 


6604)00 
6004)00 

6504X)O 


61 
61 
61 


.1032 
.0091 
.0949 


.929 
.892 
.854 


1988 
1830 
1678 


500.000 
460,000 
400.000 


61 
37 
37 


.0905 
.1103 
.1039 


.815 
.772 
.727 


1525 
1373 
1220 


960.000 
900,000 
2504)00 


37 

87 
37 


.0972 
.0900 
.0821 


.680 
.680 
.575 


1068 
915 
763 



r/ 



160 



/ 



PROPERTIES OF CONDUCTORS. 
AtaiidAMl Copper Stnuids. — (Con^tntMd). 

ROXBUNO. 



SiM. 

D% &. S* 



Wires. 



No. 



0000 

000 

00 


10 
10 
10 


.1055 
.0041 
.0837 






1 

2 


10 
10 

7 


.0746 
.0663 
.0075 




8 

4 
5 


7 
7 
7 


.0866 
.0771 
.0688 




6 

8 

10 


7 
7 

7 


.0612 
.0484 
.0386 




12 
14 
16 


7 
7 
7 


.0306 
.0242 
.0103 




18 


7 


.0151 





Site. 



OuUide 
Diameter. 



Weisht. 
Lbs. per 
1000 ft? 



.528 
.471 
.410 


645 

513 
406 


.873 
.832 
.293 


322 
255 
203 


.260 
.231 
.206 


160 
127 
101 


.184 
.145 
.116 


80 
50 
32 


.002 
.073 
.068 


20 

12 

8 


.045 


5 



IVeailMr-proof Use amd Homo fTlre. Aolid C«bA«< 

Standard Undbrqround Cabls Co. 



B. dc S. 
Gauge. 



0000 

000 

00 



1 

2 

8 

4 

5 

6 

7 

8 



10 

11 

12 

14 

16 

18 

20 



Double Covered. 



Lbs. per 

MUe. 



3690 

2070 

2300 

1860 

1500 

1225 

080 

800 

640 

520 

420 

345 

275 

235 

100 

145 

105 

80 

55 

42 



IAm. per 
1000 ft. 



600 

562 

452 

352 

284 

232 

186 

151 

121 

08 

70 

65 

52 

45 

36 

27 

20 

15 

10 

8 



Triple Covered. 



Diam. in 
MUs. 



725 
655 
585 
545 
505 
470 
385 
360 
335 
300 
270 
245 
225 
105 
180 
165 
140 
130 
125 
122 



Lbs. per 
Mile. 



3010 

3160 

2560 

2020 

1650 

1340 

1050 

860 

700 

575 

465 

300 

320 

265 

226 

180 

130 

100 

80 

68 



Lbs. per 
1000 ft. 



741 

508 

485 

382 

312 

254 

100 

163 

132 

100 

88 

74 

60 

50 

42 

34 

24 

10 

15 

12 



Diaxn. in 
Mils. 



780 

700 

635 

590 

550 

515 

450 

430 

400 

360 

335 

265 

255 

220 

205 

185 

160 

150 

145 

135 



RUBBER COVERED WIRES AND CABLES. 161 

17a««rwvMem' T«st of Sablier Govered Wir»« 

Adopted Dec 6, 1904, 



Tlie ISectrieftl Cominittee of the Underwriten National ABBooiation 
rMoamiended the foUowinc, which was adopted. 

Each foot of the completed oovering muat show a dielectric strength 
■ofBcieat to resist throughout five minutes the application of an electro* 
motive force proportionate to the thickness of msulation in aiooordanoe 
with the following table: 

Tliieknesi Breakdown Test 

m 64ths indico. on 1 Foot. 

1 8,000 Volts A. C. 

2. . . 6,000 " " 

3 9,000 " 

4 ii,oo6 •• 

6 13,000 " 

fl 16,000 " •• 

7 16,600 •• •• 

8 18,000 " •• 

10 21,000 •• •• 

12 23,600 " •• 

14 26,000 " " 

16 28.000 " •• 



I 



nl livbber Corered ITlrea and Cables. 

(Made by General Electric Company.) 

Bnbber covered wires and cables are insulated with two or more coats of 
Tobber, the inner ooat in all cases being free from sulphur or other sub- 
rtance liable to corrode the copper, the best grade of nne Para being em- 
plored. All conductors are heavily and evenlv tinned. 

nve distinct finishes can be furnished as follows: — White or black braid, 
phdn lead jacket, lead Jacket protected by a double wrap of asphalted Jute, 
lead jacket armored with a special steel tape, white armored, for submarine 



For use in conduits the plain lead covering is recommended, or if corro- 
iU>B is especially to be feared, the lead and asphalt. For use where no con- 
dvit is available, the band steel armored cable is best, as it combines 
moderate fleadblUty with great mechanical strength, enabling it to resist 
treatment which would destroy an unarmored cable. 

Id addition to the ordinary galvanometer tests, wires and cables are 
teited with an alternating current (as specified in table) before shipping. 

.Special rubber covered wire and cable with lead jackets will be covered 
viththe following thicknesses of lead unless otherwise specified: 

Outside diameter of cable (inside diameter of lead pipe). 

Up to and including . 600* A' 

JiOl'to .reO*. inclusive h' 

.751' to 1.250', inclusive h' 

1.26rtol^. inclusive ... A' 

Larger than 1.501' i' 



PROPERTIES OF CONDUCTORS. 



HatioBal HBctPtc Cml«, 



Si«. 


1 


-? 


t" 


1. 


J 


f 


i 


7^S^ 


B. * 3. 


II 


ll 


n 


ll 


IS 


IM 


20 


33 


170 


253 


A 


ft 


.000 


ISOO 


i« 


190 


35 


40 


203 


284 


ft 


ft 


IMXI 


1500 


H 


ao3 


33 


47 


220 


397 


ft 


ft 


i<m 


IfiOO 


12 


230 


43 


58 


213 


314 


ft 


ft 


1000 


IJSOO 


10 


Ml 


58 


74 


273 


335 


ft 


ft 


1000 


ISOO 


B 


ZBB 


81 


99 


318 


3S3 


ft 


ft 


1000 


IGOO 


6 


M3 


130 


lao 


389 


411 


ft 


A 


sow 


2500 


e 


372 


159 


ISO 


433 


431 


ft 


A 


woo 


2500 


- 4 


3M 


187 


210 


476 


453 


ft 


A 


2000 


2500 


9 


*I9 


830 


254 


538 


478 


ft 


A 


3000 


2500 


3 


448 


273 


298 


599 


507 


ft 


A 


aw 


3600 


1 


540 


362 


390 


722 


670 


ft 


ft 


2600 


3900 





576 


438 


«7 


981 


636 


A 


ft 


25«) 


3500 


00 


eie 


633 


582 


1116 


675 


A 


ft 


25m 


3500 


000 


961 


648 


678 


.279 


721 


A 


A 


2500 


3500 


0000 


711 


7B4 


R27 


1473 


771 


A 


ft 


250O 


3500 



ohl* Ho. 1 B. A 8 uid la 



«r ofdou 



ir diunatar of doubls 



BCBBEB IHSULATBD WIBSS AND CABLES. 



Sa. 


II 




loft. 
b*. 


11 




B.*9 ud 










li 


1 


I 


u 


1 


l« 


.196 


38 


43 


210 






.ai2 


3S 


50 






30 






4S 


63 


258 




33 


10 

s 


.355 
.2SS 


aa 

86 


107 
162 


2S8 
410 




34 

37 
43 


fi 


.3»a 


las 


IS9 


4S5 




45 




.423 


1B7 


321 






48 






240 


365 


507 




60 






280 


316 


639 




54 




.587 


S81 




935 






loom 


.eia 


M7 


478 


1030 




67 




.6M 




403 


loss 




68 


laooo 


.OH 


513 




1138 










563 


£96 


1303 




T 


liOMO 


.am 






1278 






OOO 


.721 


BS3 










smn 




8W 


834 


1532 




82 




.779 


83S 


809 


1583 




S3 


KmoD 


.873 


1032 










WOOOO 


.1)32 


1218 


1283 


2303 




01 


UOODO 






1449 


2527 






««wo 
sooooo 


1.037 


161S 


1958 


3203 




IS 


momo 








3725 




2S 


MOOT 


1,384 


2619 




4148 






TSXW 


I.32S 


3791 


2S80 


4365 






wxno 




39G9 


30S1 


4912 




4 


mnco 


1.423 


339S 










looono 


1.482 


3631 


3721 








IBOOM 


1.650 


449S 


4600 


7704 




8 


IWOOO 






5433 


8754 




94 


WOOOO 


1.W2 


0958 


7075 


10821 







3S0 


^ 


> 


1000 


306 
325 


g 


1 


1000 








1000 


379 


1 




1000 


433 






3000 


405 




sooo 


481 






aooo 


609 






3000 






i 


2000 






3S00 


676 






2500 


686 






2600 


716 






2600 


730 






2600 














i 


2500 


823 




2600 


839 








948 






4000 


008 
















103 


^ 




4000 


188 




4000 


298 


1 


















5000 


430 






6000 


580 


i 


i 


SOOO 


820 




1 


5000 


942 




SOOO 


163 


* 


5000 



ir diamMer of doubl* 



J 



164 



PROPERTIES OF CONDTTCTORS. 



TVT P& 



n«ctrlc CoaiiMuij It 

Cable (^' livbber). 

(iJBi. — Rbd Cobb, 2500 VoLim; Wbitb Cobb, 3000 Voias. 
ix>B 30 Miinrra& 

Wire. 



SiM. 
B. A. S« 



I 



16 
14 
12 
10 
8 



Diametw, 



.221 
.234 
.251 
.272 
.209 



Weight 

per 1000 ft. 

in Lbs. 



odA 



83 
40 
51 
67 
91 



.2 . 



48 
56 
67 
85 
100 



233 
249 
273 
305 






.315 
.328 
.845 
.366 
.803 



li 



§ 



i: 



Insulatioin 

ReBiotanoBin 

MeeohtDS 

perllile. 



Red 
Core. 



350 
850 
850 
860 
860 



Whita 



000 
600 
600 
600 

eoo 



Cable. 



16 


.227 


39 


56 


242 


.326 


^ 


800 


600 


14 


.248 


43 


61 


260 


.337 


A 


350 


600 


12 


.262 


60 


80 


285 


.356 


A 


850 


600 


10 


.286 


78 


99 


316 


.380 


A 


350 


600 


8 


.816 


106 


127 


360 


.395 


A 


860 


600 



NoTB. — Add -in* to lingle braid for diameter of double braid* 



RUBBER INSULATED WIRES AND CABLES. 



— Rmd Cobk, 600O Vovn; WoiTa Oobb, 0000 Voun, 



Sb>. 


Diuiats, 


p«lC&Oft. 


P. 
1_ 


4 

3 






B.A8.ud 


S 






pwMil*. 


C.H. 


n 


I 


ss. 


^^ 




.396 


81 


80 


zea 


870 


^ 


400 


~700 






313 


78 


93 


31S 


303 












3M 


90 










400 


700 






381 


116 


138 


396 






400 








414 


103 


177 


467 


474 












434 


181 




498 


494 






eoo 






400 




S3« 


646 


610 




300 


eoo 






481 


203 


SSO 


flOS 


041 


i 


360 








S40 


313 


340 


S74 


609 




eoo 










403 


013 


8S3 




860 


000 






007 


44B 


478 


103S 


■07 


f 


360 




00 




947 


643 








300 


600 


OOO 






aei 


OM 


1323 






300 


GOO 


OODO 




743 


800 


841 


1619 


803 


A 


800 


GOD 



.300 


00 


91 


304 


'Z 




400 


700 




324 






332 




400 


700 




368 


103 


120 


307 


427 




400 


700 




308 


131 


156 


410 


457 






7» 




430 






4SG 


49S 






700 




468 


203 


229 


S28 


618 




360 


800 




484 


339 


see 


683 


G23 




360 






642 














000 






830 


305 


878 


834 


iV 


380 


000 




018 


409 


438 


900 


678 


^ 


360 






047 


467 


498 


1084 . 








600 




007 


480 










360 


000 




687 


062 


G0« 


1183 


747 




300 


600 




701 


686 


618 


1255 


761 




300 






731 


638 




1339 






300 


600 




752 


709 


748 


1430 


812 


t 


300 


600 




7W 


820 


861 


16W 


864 


300 




, 


810 


804 


900 


1043 


870 


lV 


300 


600 



Br of double brv<l- 



166 



PROPERTIES OF CONDUCTORS. 



(A 



// 



Tbvt PBsee 



UBB. — Rbd Cork, 7500 Volts ; Whttb Cobb, 9000 V01.TB, 
roB 30 Minutes. 

I. Wire. 



Sue. 
B. 9 S. 



14 

12 

10 

8 

6 

5 

4 

3 

2 

1 



00 

000 

0000 




.379 
.396 
.417 
.444 
.477 
.527 
.549 
.572 
.603 
.634 
.670 
.710 
.756 
.805 



Weight 

per IWX) ft. 

in lbs. 



.£73 

18 



84 
98 
117 
144 
186 
224 
259 
300 
351 
414 
493 
591 
712 
859 



J2 . 



106 
121 
141 
169 
213 
252 
287 
329 
380 
445 
525 
625 
746 
895 



• 






372 

398 

432 

479 

547 

583 

635 

852 

933 

1028 

1142 

1282 

1450 

1649 



I 



.438 
.455 
.478 
.503 
.536 
.568 
.578 
.833 
.663 
.604 
.730 
.770 
.815 
.865 



II 



.az- 



A 

A 
A 
A 
A 
A 
A 

it 
it 

A 

A 



Insulation 

Reaifltanoe in 

Megohms 

per Mile. 



Red 
Core. 


White 

Core. 


600 


1000 


600 


1000 


600 


1000 


600 


1000 


550 


900 


550 


900 


550 


000 


550 


900 


550 


900 


550 


900 


500 


800 


300 


800 


300 


800 


300 


800 



BUBBEB INSULATED WIRES AND CABLES. 



tHamwml Mtoetoto «J*npwv JBalikMr M — l« f < CMI 
I FtMmtjam. — Bbd Cobb. 7500 Voltb ; Wnini Cobb, QOOO 




u 



373 


447 


^ 


BOO 


401 


4M 




BOO 






t 


600 


401 


S30 


900 


ses 


568 


J 


660 


eos 


580 




821 


e3« 




S60 


S96 


eos 




660 


B81 


<W7 




560 


1104 


741 




560 


110S 


770 




660 




7S0 






1290 


810 




600 


laM 


SM 




600 


1443 








IMS 


875 




BOO 


1939 


MS 




600 


leST 


064 






2178 1 


031 




400 


2444 1 


070 




400 


2872 1 








3901 1 


104 




400 


33M 1 


2E1 




360 




329 




4222 1 


401 


■ 




47S1 I 


460 




300 i 


S012 1 


498 


300 1 


6432 1 


661 




300 


5852 I 


630 


300 



SatM, — Aild ^ to sDcia braid (or diuoMar of doubla braid. 



168 



PROPERTIES OF CONDUCTORS. 



Tnr pRjBflBuiiB. — 



Cable ({k' RiaM»er). 

Rbd Cobs, 12,000 Voi/»; Whitb Cobb, 16.000 
VoxAB, FOB 30 Mznutbb. 

L Solid. 



Sise. 
B. A S* 



14 

12 

10 

8 

6 

5 

4 

8 

2 

1 



00 

000 

0000 



.534 

.551 

.672 

.598 

.682 

.652 

.674 

.609 

.728 

.750 

.795 

.860 

.805 

.945 



WeUcht 

per 1000 ft. 

ID lbs. 



£-6 

OQPQ 



156 
173 
196 
226 
272 
302 
340 
386 
441 
509 
592 
696 
851 
1011 



O u 



184 
201 
224 
255 
303 
833 
372 
419 
474 
643 
638 
732 
926 
1084 



IJS 



512 

540 

736 

792 

872 

924 

982 

1053 

1137 

1235 

1356 

1708 

1898 

2109 



\^ 



.562 
.680 

.eoi 

.668 
.692 
.712 
.734 
.759 
.788 
.819 
.855 
.926 
.971 
1.021 



a 



A 

h 
A 
A 

A 
A 
A 



Insulation 

ResiBtance in 

Mogoluna 

per Mile. 



Red 
Core. 



700 
700 
700 
700 
700 
600 
600 
600 
600 
600 
560 
550 
550 
550 



White 
Core. 



1200 

1200 
1200 
1200 
1300 
1100 
1100 
1100 
1100 
1100 
1000 
1000 
1000 
1000 



BUBBER INSTJLATBD WIRES AND CABLES. 



169 



Kleotaic Crnmtpmmj MnM^r Mmmlmtmd. IfTIre 

(A' IftaMwr) — QmUnued. 



II. Stranded. 



B. k S. and 
CM. 



14 

12 

10 

8 

6 

6 

4 

3 

2 

1 

lOOOOO 



126000 

00 

ISOOOO 

000 

200000 

0000 

250000 

aooooo 

350000 
400000 
fiOOOOO 
0OOOOO 
700000 
760000 
800000 
900000 
lOOOOOO 



Diameter, Single 
Braid. Inches. 


Weight 
per 1000 ft. 
in lbs. 




Double 
Braid. 


.543 


162 


190 


.562 


181 


209 


.586 


205 


233 


.616 


239 


268 


.654 


200 


820 


.676 


323 


354 


.702 


366 


397 


.730 


413 


447 


.762 


472 


506 


.806 


555 


591 


.850 


619 


656 


.860 


637 


676 


.800 


708 


759 


.904 


780 


844 


.924 


838 


903 


.965 


915 


981 


.997 


1042 


1110 


1.013 


1083 


1151 


1.060 


1225 


1294 


1.119 


1424 


1404 


1.167 


1600 


1675 


1.213 


1781 


1860 


1.300 


2138 


2226 


1.378 


2407 


2589 


1.450 


2854 


2950 


1.484 


8080 


3127 


1.516 


3206 


3304 


1.579 


3557 


3658 


1.638 


3000 


4004 



-8 

h 

it 





3 


524 


.572 


566 


.591 


758 


.646 


822 


.676 


012 


.714 


968 


.736 


1034 


.762 


1112 


.790 


1201 


.822 


1332 


.866 


1638 


.926 


1666 


.936 


1750 


.966 


1834 


.980 


1017 


1.000 


2032 


1.031 


2212 


1.073 


2271 


1.089 


2473 


1.136 


2745 


1.195 


2m) 


1.243 


3218 


1.289 


3679 


1.376 


4474 


1.485 


4938 


1.557 


5161 


1.591 


5384 


1.623 


5820 


1.687 


7085 


1.808 



i 
i 

A 

A 

A 
I 



Insulation 
Resistance in 
Megohms 
Mile. 



S 
6 



700 
700 
700 
700 
000 
600 
600 
600 
600 
550 
550 
550 
550 
550 
550 
550 
500 
500 
500 
500 
450 
450 
460 
400 
400 
350 
350 
350 
350 



.Sfi 



1200 

1200 

1200 

1200 

1100 

1100 

1100 

1100 

1100 

1000 

1000 

1000 

1000 

1000 

1000 

1000 

900 

900 

000 

900 

800 

800 

800 

700 

700 

600 

600 

600 

600 



( 



Hon. — Add -fg' to single braid for diameter of double bfaid. 
^or j^' insulation the insulation resistance will be in proportion with A' 
■n^A' insulation. 
"^^ pressure for A' Red Core, 10,000 toKs; White Core, 12,000 Tolts 



PROPERTIB8 OP CONDUCTORS. 



B CMaHMf T1 





TiaT PBDviuBm. — 


3000 Vol™ roil 


30 M 


MUTEB. 








L^td. 


Brmided. 


lomila. 


■ndC.M. 


II 


Mi 


i 


1 

.s 

740 


M 






iie2 




.8 


440 


600 




















1728 






9 


WH) 


653 


SOO 




1880 








OM 


7S8 


BOO 




2123 


t 




a 1 




900 






2358 






077 


1063 


500 




3847 






3 1 


230 


13S2 


600 


100000 




^ 






301 




600 




331T 




3! 1 




1633 


500 


125000 


3631 


t 




41 1 


X>ft 


1800 


GOO 




40*S 








1967 






4333 






51 1 






600 


000 


4610 






K 1 


M7 


2381 


GOO 




4968 






71 1 


tS6 


3638 


500 


0000 


6318 


A 




7; r 


66V 


2805 


600 





TutPfb.™ 


.,-8000 VOLT5 TOS 30 Mi»DT«. 






I-d«.. 


Bniid«l. 


Iiunila- 


udCU. 


i . 


t 

1 
.9 


S I 


1 


u 


Sis- 




I8S2 1 














2144 1 


IKH 




133 


796 






2332 1 


236 




170 


913 


900 




2400 I 


292 




Z36 


1029 


000 




2B26 1 


363 












3354 1 


463 


J 1 


Jt56 


1378 


900 








451 


1647 


000 


lOOOOO 


3947 1 










900 




4134 1 


MS 




SMI 




800 


136000 


4385 1 


607 




594 


3083 


800 


00 


4636 1 








3361 


800 


leoooo 


S372 1 


77(1 








800 


000 


6108 I 




t 1 


740 


2606 


800 


3OOO0O 


6500 1 






831 


2967 


800 




6SB3 2 


036 


J 1 


S6E 


3238 


800 



RUBBER INSULATED WIRES AND CABLES. 



I^VT Pbusukb, — 16,000 







LMdad. 




Br>id«d. 


'"i'Bf 


wIC.U. 


i 


1! 


pi 


11 


i 






i.3:« 








1300 




3077 


1.4M 




362 


1087 


1300 




3283 


i.S38 




440 


1224 


1300 




3488 


1-5M 


i 1 


toe 


1353 


1200 




3707 






1S36 


1300 




4046 


1.723 


J 1 


626 


ITSl 


1300 






1.818 


721 


2030 


1100 


lOOOOO 




1.043 






ZIM 


1100 





S78e 


l.BM 










115000 




2.030 




•m 


2490 


1100 


00 






1 


300 


2670 


uoo 


ISOOOO 


6677 




! i 






itoo 


000 


7013 


2.170 








MOOOO 






i ' 


101 


3421 


1100 


0000 


7S23 


2.205 


i 2 


I3J> 


3707 


1100 



T 


BTP.IB. 


™«--26 


000 VoLn roM 30 HiHim 








I«ded. 




iti, 


Ill 


1! 








1.873 








1668 


1600 




4437 


I.OflO 










1770 






4661 


3.008 








HI1 


1019 






4885 


3.064 












1500 




0710 












2281 






6535 


3.256 








im 


2405 






6005 


3.351 








IIW 




1500 


lOOOOO 


7259 


2.414 








246 


2908 






7533 


2.436 








271 


3145 


1400 


13W00 


7838 


3.500 








33S 


3354 




oo 




3.530 








3563 


1400 


uoooo 


8400 


2.576 










3813 






8SU 


3.641 








481 






attwo 


0302 














1300 


0000 


0738 


3.786 








au« 


4893 


1300 



172 



PROPERTIES OF CONDUCTORS. 



«eB«na fltoctefte GoaipaMy Bxtim ftoxil^le 

Hub is adapted for use as brush-holder leads, or to any use 
flexibility is required. The finish is Uaek glased linen braid, 
of the strand is No. 25 B. & 8. 



Eaoh wire 



I 







Dimensions in Inches. 


' Number 


arcular 
liils. 








Wires in 
Strand. 


Diameter 


Thiekness 


Diameter 






Bare. 


Rubber. 


OirerAIL 


25 


8.000 


.108 


.047 


.276 


50 


16.000 


.150 


.047 


.820 


76 


24.000 


.205 


.047 


.876* 


100 


32,000 


.235 


.047 


.460 


150 


48.000 


.285 


.047 


.600 


200 


64,000 


.325 


.047 


.640 


250 


80.000 


.350 


.047 


.600 


300 


96,000 


.385 


.065 


.666 


350 


112.000 


.425 


.065 


.706 


400 


128.000 


.460 


.065 


.740 


450 


144.000 


.485 


.065 


.765 


500 


160.000 


.570 


.065 


.810 


550 


176.000 


.530 


.065 


.830 


000 


192.000 


.570 


.065 


.870 


050 


208,000 


.605 


.065 


.935 


700 


224.000 


.625 


.065 


.966 


750 


240,000 


.640 


.065 


.970 


800 


256.000 


.680 


.065 


1.010 


900 


288.000 


.700 


.065 


1.030 


1000 


320.000 


.725 


.065 


1.066 


1250 


400.000 


.825 


.065 


1.166 


1500 


480.000 


.880 


.065 


1.213 


1750 


500.000 


.960 


.093 


1.360 


2000 


640.000 


1.060 


.093 


1.410 


2250 


720,000 


1.100 


.093 


1.500 


2500 


800.000 


1.200 


.093 


1.600 


2750 


880.000 


1.250 


.093 


1.650 


3125 


1.000.000 


1.480 


.093 


1.830 



^ 



SPECIAL CABLES. 



173 



GENERAL ELECTRIC COMPANY. 

iblaa are adapted for use as brush-holder and field leads, and for 
wiring ear bodies and oonneeting them to the trucks. 

The jumper cable is made with an outside rubber jacket protected by tiro 
braids, the outer being of the best linen thread. It is made very flexible for 
eoaneeting cars, and is designed to withstand the constant swinging with a 
auBiBunn Mwou«t of 



f^A J 


li 


1^ 

• 
8 


4 

is 
A 


Single Braid. 


Extra Braided. 


strand. 




1 






Nanbcr of wires and sise 
of wireB.ft 8. 


|5 


Weight in 
lbs. per 
1000 ft. 


Diameter 

in 

inches. 


Weight in 
lbs. per 
1000ft. 


1 j 

Q -3 


40/24 


.180 


107 


.315 


146 


.600 


49/^ 


.207 


6 


^ 


161 


.362 


200 


.600 


49/22 


.226 


4 


174 


.380 


260 


.626 


49/21 


.262 


3 


A 


205 


.407 


281 


.626 


75/25 


.206 


6 


A 


132 


.360 


186 


.600 


100/25 


.236 


5 


A 


• • • 


.390 


286 


.625 


150/26 


.285 


4 




260 


.440 


300 


.625 


200/25 


.326 


2 


A 


• • • 


.480 


446 


.760 


250/26 


.350 


1 


A 




.506 


480 


.750 


860/25 


.426 


1/0 


A 


■ • • 


.670 


555 


.750 


7/.0485 


.146 


8 


A 


103 


.280 


146 


.405 


7/.0613 


.184 


6 


^ 


138 


.339 


189 


.464 


7/.0773 


.232 


4 


A 


209 


.387 


276 


.512 


Type U Train Control 
















Siocle 19/26 .... 


.090 


12 


A 


• • • 


• • • • 


65.6 


.280 


9 GmifaKtor Tram Cable 


.000 


12 


A 


« • ■ 


« • • ■ 


600 


.940 


9 Gonduotor Jumper 
















CsbJe 


.000 


12 


A 


■ • • 


• • « • 


640 


1.030 



( 



- Sade conduoton of both train and jumper cables composed of 19/26 
B.CB. wires. 



174 



PROPERTIES OP CONDUCTORS, 



UTAVY 0XA9|]»AJB1» ^tmjrsa. 

In the following table are given uaes of Navy Standard Wires 
■pedfications issued by the Navy Department in March, 1897. 



• 


8'2 


e 


Diameter 


Diameter in 


32d8 


fe - 


• 


god 

8« 

m 


Inches. 


of 


an inch. 




< 


Over 
copper. 


Over 

Para 

rubber. 


Over 

vulc. 

rubber. 


Ova- 
tape. 


Over 
braid. 


4,107 


1 


14 


.06408 


.0953 


7 


9 


11 


56.9 


9.016 


7 


19 


.10767 


.1389 


10 


12 


14 


103 


11.368 


7 


18 


.12090 


.1522 


10 


12 


14 


108.5 


14,336 


7 


17 


. 13578 


.1670 


10 


12 


14 


115.5 


18.081 


7 


16 


.15225 


.1837 


11 


13 


15 


140 


22.799 


7 


15 


.17121 


.2025 


12 


14 


16 


165i 


30.856 


19 


18 


.20150 


.2328 


12 


14 


16 


184 


38.912 


19 


17 


.22630 


.2576 


13 


15 


17 


218 


49.077 


19 


16 


.25410 


.2854 


14 


16 


18 


260i 


60.088 


37 


18 


.28210 


.3134 


15 


17 


19 


314 


75,776 


37 


17 


.31682 


.3481 


16 


18 


20 


371 


99,064 


61 


18 


.36270 


.3940 


18 


20 


22 


463 


124,928 


61 


17 


.40734 


.4386 


19 


21 


23 


557 


157.563 


61 


16 


.45738 


.4885 


20 


22 


24 


647 


198,677 


61 


15 


.51363 


.5449 


22 


24 


26 


794 


250,527 


61 


14 


.57672 


.6080 


24 


26 


28 


970 


296.387 


91 


15 


.62777 


.6590 


26 


28 


30 


1.138 


373,737 


91 


14 


.70488 


.7361 


29 


31 


33 


1.420 


413.639 


127 


15 


.74191 


.7732 


30 


32 


34 


1.553 


Double Gonducto 


r. Plain 


, 2-7-22 I 


J. & S. . 


• • ■ 


• • • 


• » • 


181.5 


Double Gonducto 


r, SOk, 


2-7-25 B. 


AS.. . 


• • ■ 


• ■ • 


• • • 


28 


Double Gonducto 


r, DiviE 


ig Lamp, . 


2-7-20 B 


(.AS. 


• « ft 


• • • 


218.3 


Bell Cord, 1-16 E 


;. Sc8. 












20 7 





















PAPKII nSlTIiAarEO AITD I<KA]»K]» wxrbs aitd 

CABMJEII. 

GENERAL ELECTRIC 00. 

There will be found on the following pages data of a full line of paper 
insulated and lead covered wires and cables. All cables insulated with 
fibrous covering depend for their successful operation and maintenance 
upon the exclusion of moisture by the lead sheath; and this fact should 
be borne in mind constantly in handling this class of cables, consequently 
the lead on them is extra heavy. The use of jute and asphalt covering 
over the lead is strongly recommended on all this class of cables, inasmuch 
as their life is absolutely dependent upon that of the lead. Paper insulated 
cables cannot be furnished without the lead covering. 



PAP£B INSUI<ATED WIRES AND CABLES. 



175 



I. Solid. 



B. 4 a and 
CM. 



10 
8 
6 
5 
4 



A' Iiunil*tion 

Test Pressure, 4000 

Volta for 30 Minuiee. 



^9 * 

^8 



413 
461 
530 
674 
626 



-414 
.441 
.474 
.494 
.517 



^1 






A' Xxwulation 

Test Pressure, 6000 

Volts for 30 liinutes. 



^8 



493 
542 
613 
660 

716 



.477 
.603 
.637 
.667 
.679 



A 

A 
A 




300 
300 
300 
300 
300 



II. Stranded. 



6 


668 


.WD 


A 


646 


.669 


A 


250 


6 


606 


.518 


A 


604 


.681 


A 


260 


4 


662 


.644 


A 


764 


.607 


s 


250 


2 


814 


.604 


A 


1.068 


.098 


250 


1 


1.072 


.679 


A 


1.184 


.742 


A 


250 


lOOOOO 


1,176 


.708 


A 


1,289 


.771 


A 


250 





1,190 


.718 


A 


1.316 


.781 


A 


260 


125000 


1.276 


.748 


A 


1,393 


.811 


A 


200 


00 


1.364 


.762 


A 


1.470 


.826 


A 


200 


160000 


1,431 


.782 


A 


1.647 


.845 


A 


200 


000 


1.536 


.813 


A 


1,656 


.876 


A 


200 


200000 


1.703 


.866 


A 


2,046 


.949 


A 


160 


0000 


1.768 


.871 


A 


2,106 


.965 


A 


150 


250000 


2,165 


.950 


A 


2,304 


1.012 


A 


160 


aooooo 


2.435 


1.009 


A 


2,574 


1.071 


A 


160 


aaoooo 


2.660 


1.067 


A 


2,804 


1.119 


A 


125 


4000OO 


2,890 


1.108 


A 


3.041 


1.165 


A 


125 


500000 


3,029 


1.252 


i 


4.106 


1.315 


i 


125 


600000 


4,409 


1.330 


i 


4.608 


1.393 


i 


125 


7U000O 


4.876 


1.402 


i 


6,067 


1.466 


i 


100 


750000 


6.106 


1.436 


i 


6.298 


1.499 


i 


100 


800000 


6.337 


1.468 




6.623 


1.631 


i 


100 


900000 


6.782 


1.581 


i 


6.976 


1.694 


i 


100 


lOOOOOO 


6,213 


1.690 


■J- 


6,416 


1.663 


i 


100 


1250000 


7.293 


1.727 


1 


7.600 


1.790 


i 


100 


1500000 


8.329 


1.840 


i 


8.542 


1.912 


i 


76 


2000000 


10.866 


2.060 


It 


10.686 


2.132 


* 


50 



PS0PERTIE8 or GONDDCTOK8. 



rmmmr 

I cAi«. 









1 ,. 








Bp\^ 


4 


^ 


h 


n 


?i 


l^ 


s 




U 


i 


U 


n 


S.9 


|3 


-9 ^ 


10 


678 


.030 


iV 


etw 


.603 


A 


40O 


s 


632 


.S«5 


iV 


87fi 


.6S9 


A 


*00 


e 


707 


.S09 


iV 


960 


.693 


A 




6 






t 


1,011 




g 


40O 


* 


003 


,673 


1,078 


.738 


400 

















i 


egg 


716 




400 


943 


674 


1,056 


737 


1 


400 


i,oia 


700 




1,1S4 




400 








1,800 


833 




360 


1,300 


804 




1.420 


867 




360 


1.407 


S33 




1,639 


896 






1,433 






1,566 


906 




360 


1.618 


878 




1.762 


967 


j 


360 


1.693 


887 




1,049 


981 


300 


1,802 








001 




300 


2006 


970 




3,147 1 


033 




300 


a,lB7 1 


01! 




3,330 1 




A 




2,246 I 






3,390 1 


090 


^ 


250 


3.451 1 


076 




Z897 1 


137 






a.734 1 


134 






269 






a,9B8 1 






3,716 1 


307 






8.796 I 


290 




3,980 1 


363 






4.29f) 1 


377 






440 






4.793 1 


i&6 




4,983 1 








5,209 I 


E27 


I 


5,463 1 


890 






5.600 1 






624 






6.721 1 


639 






666 






«.189 1 


666 


j 


6,390 I 


719 






e.63i 1 


716 


6,838 1 


778 










j 


7,943 1 








8.776 I 




9,001 3 








10,834 2 


IM 


i 


11,066 2 


367 







PAPER INSULATES VHtES AND CABLES. 



D«w»a cSSmi. 





T«t Prwin. ie,60O 




i 








C.H. 


k 


Bi 


l=- 




IM 


"5 = 






1.IB7 


.S20 


t 


1,770 


1.030 




eoQ 




1.223 




fm 


1,S46 


i.oeg 




SCO 




1.313 




fWl 




1,0« 


LOW 




BOO 




1,309 




mt 




3.013 


i.iie 




5G0 




1.868 




953 


iV 


%080 


1.141 




eeo 



< 



n. BtrudMl. 





1.357 


003 


■ ' 


3.001 1 


121 




600 




1.63B 


OSS 




2,008 1 


143 


600 
















600 




l'.917 1 


0*1 


■ ■ 


2.e6S 1 


2B2 




600 




aJ3B2 1 


OSS 






330 






Mnooo 


2,17B 1 






3,207 1 






4S0 





3.204 1 






3.800 1 


376 




460 


usooo 


!l.aB3 1 


164 




3.404 1 


406 




4S0 


00 


3.3S2 1 


168 




3.608 1 








lEOOOO 


3.063 1 






3.610 I 


430 




480 




3,2ie 1 


383 




3,766 1 


470 




460 


noooo 


8.400 1 






8.970 1 






40O 


oooo 


3.473 1 


340 




4.046 1 








3S000O 


3.70« 1 


387 




4.203 1 


676 




400 




4sm 1 


440 




4.811 1 


034 




400 


asoooo 


a.393 1 


4« 




4.8S8 1 






360 


«»0OO 


4,6» 1 


640 




6,108 1 


738 




360 


wnoo 


6,088 1 


037 




6,707 1 


816 




300 


«aoooo 


SM* 1 


708 


j 


0,328 1 


803 




soo 


TDOOOO 


8,087 1 


777 


0.740 1 


see 




300 


noooo 


8.331 1 


Sll 




e.as3 1 


BOB 




300 




0,666 1 






7.334 3 


031 




800 


mooo 


7.040 1 


SOS 




7.708 2 








UOOQOO 




SOS 




8.171 3 


163 




aso 


13S0OOO 


8.808 3 






9,334 2 


290 




200 


UOQOOO 


B.703 3 














mnooo 


11.810 2 


443 


I 


12,670 a 


031 




160 



PROPERTIES OP CONDUCJrORS. 






TbtP 


nacRB. 3000 Vo 


LTBTO 


^ 


Tmt Pucuhrb. SOOO Voub 




30 AiNDTM. 






FOB 30 MiNims 




B. « S. and 


1 


ll 


■^i 


%i 


1 


i 


J^ 


] 


C. U. 


1^ 


ji 




i 


i 


s 


ii 


8 


138S 






150 




■cot 




30O 




18T4 














ITS 










12S 




182 




175 




2270 


l!o83 




125 




218 




175 


2 


2837 










346 




IM 






1,314 










j 


ISO 




3035 


1.437 




100 




504 


150 





3SM 














160 


125000 




1.634 












ISO 




4420 


1.653 




100 




823 




12S 


150000 


4750 










063 




126 


000 
















I2S 




6300 


1.815 


i 


100 




879 




135 


0000 


0700 




j_ 




r» 


\_± 


filtt 




125 


■Tan P 


■ButntE, 15.000 


VOLTB 




nPtaa 


yiiSSS"-- 




ran 30 Hindt» 














~A~~ 
















319B 




A 


300 




742 2 


100 








6 


3422 




A 


275 




020 2 


150 






400 


4 


3646 










299 3 


208 






400 


2 








278 




052 S 


835 






400 




4708 


1.837 




275 




581 2 


433 






S50 


100000 




I.S63 








883 3 


495 






360 










275 






618 






850 


I2S000 


6433 


2.040 




275 




493 2 


580 






360 


00 


6766 










841 2 


908 






350 








250 




246 2 








350 


000 


7513 


2.190 




250 




057 2 


730 








200000 


7»80 


2.208 








160 2 


806 






3O0 


0000 


S44fl 


2,315 




250 




983 2 


845 






300 



Thlakne»o[ mndotio 


nfn 


r3000 V 


?s 






S-: 


"* 




15 000 




itor. A' I»P« oym 


for 


38.000 V 











CAUBRIC INSULATED WIBES AND CABLES. 



WoaEiHo PanaoBE, t.OOO Vova ok Low. 
TsBT PbBBcsb, 3,000 Vovn. 



Braided. 


Laded. 


W^hl in 


Weight ia 






^r^K^ (t. 


1000 ft. 



I>iq>lci «bl« Imr^t* thw 2SO.00O Cm. »n diffisult to hwdlfl and thers- 

■n» fourth colunui — Dik. in Inches — is the over-mil dinineter of the 
Uriwd oiljli and la iv>pn>xlni»tal}' tbs mas for (itber btaided or leaded. 



PSOPBBTIBS OF CONDUCTOB8. 



WoBKora PuaanxB, S.OOO Voun o* Ln*. 



Thiok. 
LwliD 



Brudsd. 

Wsichtin 

1000 ft. 



400.000 

eoo.000 

TSO.OOO 
1.000,000 
1.260,000 
1. 100,000 
2,000.000 



2;673 
3,14S 
3,817 
4.7M 
S.TBS 



Duplax ublaa largai than 290,000 Cm. 
therefon are not noomnModed . 

Ill* fourth oolumn — Dia. in tushea — is (he c 



diffioult to bi 

ov«r-all diuuv 
biaidodoi 



CAMBRIC INSULATED WIRES AND CABLES. 



a PsMaimB, 5,000 Voun om L 
■T Pbhsumb, la^SOO VoLia. 



TWet Tbiek. 



Inohn. Iiuhn. 



BraidMt. 
Dik. ID Wnght in 
Lidn Lba. 



2100 
2347 
2Gfi« 



-fl difficult to handle and tbere- 



— M«. in Ineh«« — 



r 



182 



PROPERTIES OF CONDUCTORS. 



ITandAlMd 



Working Pressttrk, 7,000 Volts ob Lbss. 
TsBT PsESSURB, 17.500 Voivre. 



) 



Size. 
B. A S. and C. M. 


Thick, 
Ins. in 
Inches. 


Thick. 
Lead in 
Inches. 


I>ia.in 
Inches. 


Braided. 

Weight in 

Lbs. per 

1000 ft. 


Leadarl. 

Weight in 

Lbfl. pa* 

lOOO ft. 


6 Sol. 


A 


A 


.68 


320 


851 


4 Sol. 


A 


A 


.72 


380 


058 


est. 


A 


A 


.70 


336 


884 


4 St. 


A 


A 


.76 


413 


1002 


2 St. 


A 


A 


.81 


620 


1164 


ISt. 


A 


A 


.88 


605 


1505 


1/0 St. 


A 


A 


.05 


730 


1871 


2/0 St. 


A 


A 


1.00 


860 


2047 


3/0 St. 


A 


A 


1.05 


1003 


2254 


4/0 St. 


A 


A 


1.11 


1175 


2506 


250.000 




A 


1.15 


1317 


2718 


300,000 


H 


A 


1.24 


1565 


3003 


400.000 


a 


A 


1.36 


1064 


3627 


500.000 


A 




1.46 


2364 


4161 


760,000 


4s 


n 


1.67 


3264 


5707 


1,000.000 


A 


i 


1.85 


4155 


7279 



Daplex cables larger than 250.000 Cm. are difficult to handle and there- 
fore are not recommended. 

The fourth column — Dia. in Inches — is the over-all diameter of the 
finished cable and is approximately the same for either braided or leaded. 



1 



CAMBRIC INSULATED WIRES AND CABLES. 



183 



WoKKiNQ PRsasimx, 10,000 Volts ob Lbm. 
P&BMmiB, 25,000 Voun. 



Siae. 
B. k S. and 
CM. 


Thick. 
Ins. in 
Inehes. 


Thick. 
Lead in 
Inches. 


Bia. in 
Inches. 


Braided. 
Weight in 
Lbs. per 
1000 ft. 


Leaded. 
Weight in 
Lbs. per 

1000 ft. 


6 Sol. 


i 


A 


.80 


424 


1063 


4 Sol. 


A 


.84 


408 


1176 


est. 


■ ■ 


A 


.82 


441 


1102 


4 St. 


• ■ 


•h 


.87 


521 


1227 


2 St. 


y 


A 


.00 


712 


1651 


ISt. 




A 


1.04 


703 


1925 


1/0 St. 




A 


1.08 


801 


2182 


2/0 St. 




A 


1.12 


1009 


2365 


3/0 St. 




A 


1.17 


1150 


2580 


4/0 St. 




A 


1.23 


1327 


2839 


250.000 




A 


1.28 


1483 


3058 


300.000 




A 


1.88 


1707 


3353 


400.000 






1.48 


2087 


4031 


£00.000 




X 


1.57 


2467 


4709 


750.000 


1 


n 


1.80 


3458 


6470 


1.000.000 


i 


1.96 


4386 


7688 



( 



Dovlex caUea laxser than 250.000 Cm. are difficult to handle and there- 
fare are not reoomxnended. 

TIm foorth oohimn — Dia. in Inohee — is the over-ail diameter of the 
bnfaed cable And ia approziiiiately the same for either braided or leaded. 



184 



PROFEBTIES OF CONDUCTORS. 



W« 



WOBKDrO 

Tmn 



) 



listed CtaiftlM.— Ma«le 

K, 16,000 VoLom OK 
PftaBSmus, 83.000 Voxab. 



SiM. 
B. &. 8. and 


Thick. 
Idb. in 


Thick. 
Lead in 


DUkin 


Braided. 
Weight in 


Leaded. 
Weight in 


CM. 


Inch«8. 


Inches. 


Inches. 


Lbs. per 
1000 ft. 


Lbe. per 
1000 ft. 


6 Sol. 


u 


A 


1.06 


660 


1039 


4 Sol. 




•: • 


A 


1.10 


767 


2084 


est. 




■1 • 




1.08 


705 


1994 


4 St. 




•1 ' 


A 


1.12 


797 


2163 


2 St. 




A 


1.18 


927 


2373 


ISt. 


• 


■ 


A 


1.29 


1110 


2098 


1/0 St. 


■ 


• 


A 


1.83 


1225 


2860 


2/0 St. 


, 


• 


A 


1.87 


1360 


3061 


3/0 St. 


■ 


• 


A 


1.42 


1538 


3288 


4/0 St. 


1 


• 


A 


1.48 


1732 


3562 


250,000 


. 


■ 


i 


1.63 


1901 


3795 


300.000 




■ 


1.63 


2130 


4487 


400.000 


f 




1.73 


2530 


6246 


500.000 


1 


I 


1.82 


2930 


6006 


750.000 


tt 


4 


2.05 


3998 


7468 


1,000.000 


* 


2.23 


6006 


8d36 



Duplex cables larger than 260,000 Cm. are difficult to handle and there- 
fore are not recommended. 

The fourth column — Dia. in Inches ~- is the over-all diameter of the 
finished cable and is ^;»prozimateiy the same for either braided or leaded. 



CAHBBIC IN8TTLATBD WIRBe AND CABLES. 



WdkUHa PmiiaiFmB, 1.000 Voun oa I w. 
1. 3.000 Voum. 



Six. 

B. A&ud 

aM. 


TUcsk. Ins. 
inlnch». 


TTiiA- 


Inclua. 


ll-.I»r 


Laded. 

WBishtiD 

LbM» 




'■"^ 




1000 ft. 


1000 ft. 


; 


U 


J 


.87 


z 


1034 


1 






1.17 


1340 


2437 


I/O 


J 1^ 


g 


1.34 


1480 
1781 


31S2 




i J 


Jj 


l.« 

1.58 


3144 


30S9 
4536 


4/D 


* i 








S331 


190.000 


i 


1,97 


3784 


7107 



WoaEDia Pkihdu. 3.000 Voiob oa 
TiBT .PanaiiBB. 7i>00 VoLie. 





s^ 


A 1 


fW 


804 


1837 








1029 


2170 




1 i 




27 


1384 


3679 










3343 








«) 


1W4 


38S3 


3/0 


1 A 




BO 


2354} 




3/0 




7R 


2S31 


B172 


4/0 


i 




3504 


flS24 


1»M» 


i A 


07 


3083 


7498 



9 Gnt eoluom is the 
:h eoBdoctor'aiid the second eotumn !■ the thici 
iltiiiui — DU. In Inohaa — in the over-all dia 



186 



PROPERTIES OF CONDUCTORS. 



Working PasasuBB, 5,000 Vouis cm Lbm. 
Tbbt Pbbbsubs. 12,600 Volts. 



) 



Sise. 
B. A S. and 


Thick. Ins. 
in Inches. 


Thick. 
Lead in 
Inches. 


Dia.in 
Inches. 


Braided. 
Weight in 
Lbs. per 


Leaded. 
Weight in 
Lbs. per 










1000 ft. 


1000 ft. 


6 


A-A 


A 


1.20 


956 


2419 


4 


A-A 


A 


1.30 


1204 


2804 


2 


A-A 


A 


1.43 


1601 


S361 


1 


A-A 


A 


1.56 


1916 


8834 


I/O 


A-A 


A 


1.64 


2221 


4268 


2/0 


A-A 


A 


1.74 


2608 


4792 


3/0 


A-A 


i 


1.91 


3083 


6287 


4/0 


A-A 


i 


2.03 


3650 


7090 


250.000 


A-A 


i 


2.13 


4118 


7755 



WORKINa PBBBStTRB, 7,000 VOLTB OR Ll 

Tbbt Pbbbsure, 17,500 Voum. 



6 

4 
2 



1/0 
2/0 
3/0 
4/0 
250.000 



»-4 


A 


1.42 


1304 


3056 


i-i 


A 


1.53 


1583 


8473 


i-i 


A 


1.66 


1979 


4057 


i-i 


i 


1.81 


2268 


5296 


i-i 


i 


1.89 


2602 


5783 




i 


1.99 


3001 


6364 


i 


2.10 


3597 


7169 


i-i 


i 


2.23 


4077 


7890 


i-i 


i 


2.33 


4610 


8697 



Under "Thickneaa of Insulation '* the first column is the thickness of 
insulation on each conductor and the second coKunn is the thickness over all. 

The fourth column — Dia. in Inches — is the over-all diameter of the 
finished cable and is ^proximately the same for either tvaided or leaded. 



CAMBBIC INSULATED WIRBS AND CABLES 



* -"ti— *— - I— l««aJ CMilM. — Triple 0*i 

WoaKiHa Phbwuib, 10,000 Vomb <■■ L^h. 

Tut pBaauKE, 25,000 Volt*. 











Bnidad 




B.A&HK1 


Thiek. Ids. 
in Inchs. 


iDcfaa. '" 


ha. 


Weight in 
Lb». pet 
1000 ft. 


Wrighl in 
Lb..P« 
1000 It. 






i 


1 1 


ez 

73 

so 


1833 

1030 


38S1 

4713 












3860 


0433 










10 


3222 


6M3 


a/0 








2B 


3000 




J/0 








40 


11BS 


8343 




1 






S2 


4851 


eisa 


tsoooo 


i 


j-a 




oa 


5405 


0933 



WoKKJHa PaXHDBE. 16,000 VoLTfl 

Ttot PaEHDBi, 33,000 Vol 





1^ A 


1 


82 


3005 


4.2S9 




ll . 






4.744 




1 






30 


2768 

3320 


9,305 
7,2H 


1/0 








39 


3715 


7303 


2/0 












8.485 










S» 


4731 


a.aoi 


4/0 








72 


6406 






^ 






82 


6B82 


10,851 



Undw "Hucknw ot ImnilatioD" the fint column is (he Ibkkqen of 
innliboa OQ each conduetor »nd the seconJ coluEon ia the thickoesa over all. 

The foonh oolumn — Di*. in Inches — is tho overall dinmeter of the 
faiiihcd cable and is approionuitely Che name for either bruded or leaded. 



188 



PROPERTIES OF CONDUCTORS. 



BUtmrnHMmA for llMtoiyr^i 



w JLmtUa Um. 



I 



The ioBulation of these oablee is dry pi^Mr. The foUowiog qMoifioatioiie 
have been adopted by the larcer telephone oompaniee wid» therefore, loay 
be considered standard* 

€;al>le Coadvct^r. No. 10 B. and S. G.. 08% oonduotivity. inrnilatfij 
with one or two plater tapes; conductor twisted in pairs; one of the pain 
to have a distinctive colored paper for marker; len^^th of twist not to exceed 
3'. Pairs to be laid up in reverse layers; insulation to be unsaturated ex- 
cept two feet from each end to prevent moisture from entering. The lead 
sheath to have an alloy of 2^ to 3\% of tin; thickness of sheath A* for 
fifty pair of cables, /b* for one hundred pair of cables, and ^' for iaiKsr 
sixes. Insulation resistance to be at least 100 mecohms per mile after Uie 
cable is laid and spliced. Electrostatic capacity no greater than .054 with 
a maximum of .060 microfarads per mile. 

The aeHal cables for telephone companies usually follow the same speci- 
fications as those for underground use, being purchased with the ultimate 
intention of being put underground. Gables that are to remain overhead 
indefinit^y are usually made with a lighter sheathing of lead than tlwt 
specified for underground work. 



Number Pairs. 


Outmde Diameters. 
Inches. 


Weights 1000 feet. 
Pounds. 


1 


^ 


214 


2 


# 


302 


3 


* 


515 


4 


A 


620 


5 


t 


747 


6 


H 


877 


7 


■ i 


012 


10 


' i 


1.214 
1,375 


12 


i V 


15 


1 


1.566 


18 


IJ^ 


1.758 


20 


l4 


1.040 


25 


iX 


2.332 


30 


l£ 


2.748 


35 


1» 


2.085 


40 


^f' 


3,176 


45 


11 


3.365 


60 




3.678 


55 


11 


3.867 


«0 


If 


4.055 


65 


IH 


4.241 


70 


2 


4,430 


80 


2| 


4,804 


00 


2< 


5.180 


100 


« 


5,505 



SUBMARINE CABLES. 



189 



for V: 
C»r 



▲erial Vae. 



The xnautaifcion of these cables is made of a compound containing not 
hm than thirty per cent pure Para rubber. These specifications may be 
oooaidered standard, being used by the principal telegraph companies. 



¥»SMlMtf»J Aerial Vel«gT«ipli Cable. 



GngeB.ft8. 


No. of Conductors. 


Outside Diameter. 


Weight per 1,000 ft. 


14 
14 
14 


7 
10 
19 


li^ 


426 lbs. 
600 lbs. 
8^ lbs. 



i 



GoDduetors No. 14 B. and S. insulated to diameter of 6-32', cabled 
toieUier and covered with a rubber tape, one layer of tarred jute, a rubber 
tspe, sad a heavy cotton braid saturated with waterproof compound. 



•mBHAJtXlVS CAJBI.KA. 

Hmss faf4<Mi are insulated with a rubber compound containing not less 
tfasa thirty per cent (30%) of pure Para rubber. 

Tbese specifications have been adopted by the various telegraph com- 
psnia and the United States Government for general use. 



No. of 

Coadae- 

(OCB. 


Gauge of Con- 
ductors. 


No. of 
Armor 
Wires. 


Gauge of Armor 
iVires. 


Outside 
Diameter. 


Weight 

per 1.000 

feet. 


I 
2 
3 

4 
5 
• 

7 
10 


14 B. ft a 
14 B. ft 8. 
14 B. ft 8. 

14 B. ft 8. 
14 B. ft 8. 
14 B. ft & 

14 B. ft & 
14 B. ft 8. 


12 
10 
14 

16 
19 
21 

21 
22 


8 B. W. G. 
8 B. W. G. 
6 B. W. G. 

6 B. W. G. 
6 B. W. G. 
6 B. W. G. 

6 B. W. G. 
4 B. W. G. 


i' 


1150 
1675 
2400 

2760 
8100 
3600 

8600 
4600 



GoBdaetors built up of 7 No. 21 B. ft S. copper wires, heavily tinned. Each 
wadaetor Insulated with A" Rubber and Taped. 

ne above specifications refer only to river and harbor cables. Ocean 
Okies are of an entirely different character, and consist of Shore End, In- 
Wnaediate and Deep 8ea Types. 



PHOPEBTIES OP CONDUCTORa. 



■ KbMmv Wmamlmtm* ObMm. 



Upe, uid bare ilie t 



a ths metdl oarrfully by m 
or w)iD Bumpeper. 

Mmtml JtoUit.— If solid oonductor, louf lb* ends with ■ file » u ta 
give k good iont eoniact mrfacB (or Boldering, K oonduciot ia sInuidHL 
carefully apnad apart the itianda, outting out lh» cmun » cooduotom 
can be butted (ocethar, the louee ends inUrlaaitic an in Pig. 1, and bind 
•rirei down tight as in Fig. 2. witb gn or other plien. Solder wefully. 



uniw no acid; resin ia the b«t, althotiifa jc 
candle as beins handy to UM and eaey to pro* 
Aoldeied by dipi^ag Che joint into a pot of mi 
molten metal over tt 




be insulated aa previously dooribed. 



r ebo* a atyle of oo 
lolder; when dry a 




JOINTS IN CABLES. 191 

_^ tMe ^•Ibc— Jointers must have absolutely dry and 

E hands, and all tools most be kept in the best possible condition of 
[ness. Clean the Joint carefully of all flux and solder ; scarf bacli: the 
r insulation like a lead-pencil for an inch or more with a sharp knife. 
Ohiefully wind the joint with three layers of pure unvulcanised rubber, 
~ 1^ care not to touch the strip with the hands any more than neces- 
; orer this wind red rubber strip ready for yulcanizing. Lap the tape 
k tlw taper ends of the insulation, and make the coyerms of the same 
r as the rubber insulation on the conductor, winding even and 
OoTcr the rubber strip with two or three layers of rubbw-saturated 



^Tertrnf. — If the insulation is covered and protected by lead, a 
kxise sleeve is slipped over one end before jointing, and slipped back over 
the joint when tne insulation is finished, a plumber's wiped joint being 
■ade St the ends. 




Fio. 9. 

VelHta l» Wavlnir Cable*.— This cable Is covered with cotton, 
tkoronghly impregnated with a composition of hydro-carbon oils applied at 
U|b temperature, the whole beina covered with lead to protect the iusula- 
tioo. Thelnsnlating properties of this covering are very high if the lead is 
knt intact. 

Metai joints are made as usual, and a textile tape may be used for cover- 
iag the bare copper. A large lead-sleeve is then drawn over the joint, 
and viped onto the lead covering at either end : then the Interior space is 
filled with a compound similar to that with which the Insulation is im- 
pregnated. 



. ^per t— latid Cablea. — This cable is covered or 

luslated with narrow strips of thin manila paper wound on spirally, after 
vh&eh the whole is put into an oven and thoroughly dried, then plunsed 
late a hot bath of resin oil, which thoroughly impregnates the paper. This 
iasoktion is not the highest in measurement, but the electrostatic capacity 
b lev Bud the breakdown properties high. When used for telephone pur- 

C«s Uie piqper is left dry, and is wound on the conductor very loosely, thus 
▼ing Ivge air spaces and giving very low electrostatic capacity. 
Joints are made as in the waring cable by covering the conductor with 
paper tape of the same kind as the insulation, then pulling over the lead 
■leere, which is finally filled with parafflne wax. 



^ — A new joint for stranded or solid conductors is made 

by Dosw irt Sc Company, of 59 Fulton Street, New York. It is said to have 
a BMcfaaaical strength exceeding 75% of that of the cable itself, and an 
eleetriesl conductance in excess of that of the cable. 

The joint for stranded conductors consists of (see Fig. 10) a compressor 
ant **&," an outside ring "b,'' an inside ring *'c,'^ and a nipple "d.'^ The 
iBStthree parts are in duplicate. 

Jm joint is applied as shown progressively in Fig. 10. The wire is first 
■v^ppedfor a space A of an inch longer than the compression nut. The 
MBqwenon nut and the outside ring are then slipped on, being driven 
>^M with a steel driver provided for the purpose. The outer strands are 
tftt separated and the inner ring slipped on over the central core and 
skD dnyea home with a special driver. The outside strands are then 
|)Boulded back into ix>sition and the nipple is screwed in place still further 
m fonniBg the joint into shi4>e. 



I 



PROPEBTIEIS OF a 



mftcr the luhliL. 

By unettinc 

tba ■phViilov*, 




Fro. 12. AHsinbly. 

(ubttuitial hooli, oanfulty nukchinad ta 
of the ioint. The ahuk of the hook ii 

nlptils of the Randiird DgaMri joint for 

feuLlAbJy nbmped CASting. wtuch fit* in the epuia bi 
hue of the hnok, ii held in pliuie hf mevu of ■ nom 



JOINTS IN COPPER WIRES. 



193 



jr^latlair C(«tte-P«v«ha Covered frir«« 



the gutta-peroha for about two inehcs from the ends of the 
whieh are to be jointed. Fif. 14. 



Fio. 14. 

If«ct mes tiie wires midway from the gutta-pereha, and grasp with the 
fig. 15. 




Fio. 15. 

Thea twist the wires, the overiapping right-hand wire first, and then, 
letvetsiu g the grip of the pliers, twist the left-hand wire over the right. Cut 
^ the BuperanoQaendflof the wires and solder the twist, leaving it as shown 
in Fig. 16. 



( 



Fio. 16. 

Next warm up the gutta-percha for about two inches on eadi side of the 
twist. Then, first draw down the insulation from one side, half way over 



Fio. 17. 

the twisted wins. Fig. 17. and then from the other side in the same way. Fig. 
1& 



Fig. 18. 

Then tool the raised end down evenly over the under half with a heated 
{too. Then warm up the whole and work the "drawdown" with the thumb 
md forefiiicer until it resembles Fig. 10. Now allow the joint to cool and set. 



Fio. 10. 

Next roagjien the drawdown with a knife, and place over it a thin eoating 
of Ghatterton's compound for one inch, in the center of the drawdown, 
which is also allowed to set. 

Next cut a Uiick strip of gutta-percha, about an inch wide and six inches 



194 



PBOPERTIE8 OF CONDUCTORS. 



long, and wrap thlB, after it has been well warmed by the lamp, evenly OTer 
the center of the dvawdown. Fig. 90. 



Flo. 20. 

The strip is then worked in each direction by the thumb and forefinger 
oyer the drawdown until it extends about 2 inches from oenter of draw- 
down. Then tool over carefully where the new insulation Joins the old, 
after which the ioint should be again wanned up and worked with the fore- 
finger and thumb as before. Then wet and soap the hand, and smooth and 
round out the joint as shown in Fig. 21. 



Fio. 21. 

Between, and at e.Tenr operation, the utmost care must be ezerolMd to 
remove every particle of foreign matter, resin, etc. 

NoTB. Cbatterton's compound consists of 1 part by weight Stockholm tar; 
1 part resin; 8 parts Qutta-percha. 



Pliyalcal Cmwtamta •f CoMincrctally (<»•%) 



Per cent Conductivity (Copper 100) 

&>ecifio Gravity 

Founds in 1 cubic foot 

Pounds in 1 cubic inch 

Pounds per mile per droular mil 

Ultimate strength. 



sq. m. 



Modulus of Elasticity, .- 



lb. X in. 



m. X aq. m. 

Coeffident of Linear Expansion per ^C. 

Coefficient of linear Eximnsion per ^ F 

Melting Point in *»C 

Melting Point in "^F 

Specific Heat (watt-eeconds to heat lib. l** C.) 

Thermal Conductivity (watts through cu. in. temperature grad- 
ient,l*0.) 

Renttance 

Microhms of centimeter cube at 0^ C 

Microhms of inch cube at 0* C 

Oluns per mile>foot at 0^ C 

Ohms per miMoot at 20^ C 

Ohms per mile at 0** C 



Ohms per mile at 20®C. . . . 

Pounds per mile-ohm at 0^ C. . 
Pounds per mile-ohm at 20^ C. 
Temperature coefficient per " C. 
Temperature coefficient per * F. 



2.68 

107 

.0007 

.00481 

26.000 
0,000.000 



.0000281 
.0000128 

025 
1157 

402 

36.5 



2.571 
1.012 
15.47 
16.70 
81.700 

(dr. mils 
88.200 

oir. mils 

808 

424 

.004 

.0022 



1 



ALUMINUM WIRE. 



Ids 



Ahnnmmn wire of 62% conductivity is the generally accepted standard. 
Atnminum d 92% c(»duotivity. bought at 2.18 times the price of cop- 
per per pound, will give the same length and conductivity for the same 



r for Mq««l "Mj^mt^tM 






Cost per 
of Copper of 100 


Pound 


Cost per Pound 


% Conductivity. 


of Alurainnm of 62% Conductivity. 


14 cents 


28.8 cents 


15 


*■ 


82.0 


•« 


16 


M 


84.1 


i« 


17 


• I 


36.2 


•• 


18 


t* 


38.4 


•• 


19 


■• 


40.6 


•• 


20 


M 


42.6 


•• 


21 


M 


44.7 


•• 


22 


M 


46.8 


tt 


23 


M 


40.0 


•• 


24 


M 


51.1 


•( 



25 



53.2 



tfTitt< 



m for 



i of Tariova 
CondnctlTfttj 



Metal. 


Conduc- 
tivity. 


Cross 

Section. 


Weight. 


Breaking 
Weight.' 


Price 
per lb. 


Copper .... 


100 


100 


100.0 


100 


100 








54 


180 


54.0 


85.1 


185 


M 






55 


176 


53.0 


83.5 


180 


•4 








56 


173 


52.0 


82.0 


192 


M 








57 


170 


51.1 


80.6 


196 


M 








58 


167 


50.2 


79.2 


199 


•• 








50 


164 


49.4 


77.9 


203 


N 








60 


162 


48.6 


76.6 


206 


m 








61 


150 


47.8 


75.3 


210 


m 








62 


157 


47.0 


74.1 


213 


m 








63 


154 


46.3 


72.9 


216 



* Breaking weights (i)ound8 to break wire of equal conductivity) are cal- 
culated on tne assumption of an ultimate strength of 55,000 pounds per 
sqpiare inch for copper and 26,000 pounds per sqiuure inch for aluminum* 



196 



PROPERTIES OP CONDUCTORS. 



XWble«r 



ieakttmmm^m of Solid AlmMiai 
CondnctiTitj.* 

PiTTSBUBa Rkddction Oo. 



Oooducimty 02 in., the Matthiessen Standard Scale. Pure 

weighs 167.111 pounds per cubic foot. 



¥ 




ResistanceB at 70** ] 


F. 


LogcP. 




OoS 


R 








LoeiL 


IS 


Ohms per 
1000 Feet. 


Ohms 
per Mile. 


Feet 
per Ohm. 


Ohms per lb. 






0000 


.07904 


.41730 


12652. 


.00040985 


5.325516 


V. 897847 


000 


.09966 


.52623 


10034. 


.00065102 


5.224808 


,.998521 


00 


.12569 


.66362 


7956. 


.0010364 


5.124102 


1.099301 





.15849 


.83684 


6310. 


.0016479 


5.023394 


T. 200002 


1 


.19982 


1.0552 


5005. 


.0026194 


4.922688 


T.30063B 


2 


.25200 


1.3305 


3968. 


.0041656 


4.821980 


X. 401401 


8 


.31778 


1.6779 


3147. 


.0066250 


4.721274 


,.502127 


4 


.40067 


2.1156 


2496. 


.010631 


4.620666 ;. 602787 


6 


.50526 


2.6679 


1975. 


.016749 


4.519860 T.703515 


6 


.63720 


3.3887 


1569. 


.026628 


4.419152 


X.804276 


7 


.80350 


4.2425 


1245. 


.042335 


4.318446 


T. 004986 
0.006662 


8 


1.0131 


5.3498 


987.0 


.067318 


4.217738 





1.2773 


6.7442 


783.0 


.10710 


4.117030 


0.106293 


10 


1.6111 


8.5065 


620.8 


.17028 


4.016324 


0.207122 


11 


2.0312 


10.723 


492.4 


.27061 


3.915616 


0.307763 


12 


2.5615 


13.525 


390.5 


.43040 


3.814910 


0.408494 


18 


3.2300 


17.055 


309.6 


.68437 


3.714202 


0.600203 


14 


4.0724 


21.502 


245.6 


1.0877 


3.613496 


0.609860 


15 


5.1354 


27.114 


194.8 


1.7308 


3.513788 


0.710574 


16 


6.4755 


34.190 


154.4 


2.7505 


3.412082 


0.811373 


17 


8.1670 


43.124 


122.50 


4.3746 


3.311374 


0.912063 


18 


10.800 


54.388 


97.15 


6.9590 


3.210668 


1 .012837 


19 


12.985 


68.564 


77.06 


11.070 


3.109960 


1.113442 


20 


16.381 


86.500 


61.03 


17.596 


3.009254 


1.214340 


21 


20.649 


109.02 


48.44 


27.971 


2.908546 


1.314899 


22 


26.025 


137.42 


38.4 


44.450 


2.807838 


1.416301 


23 


32.830 


173.35 


30.45 


70.700 


2.707132 


1.616271 


24 


41.400 


218.60 


24.16 


112.43 


2.606424 


1.617000 


25 


52.200 


275.61 


19.16 


178.78 


2.505718 


1.717671 


26 


65.856 


347.70 


15.19 


284.36 


2.405010 


1.818595 


27 


83.010 


438.32 


12.05 


452.62 


2.304304 


1.919130 


28 


104.67 


552.64 


9.55 


718.95 


2.203696 


2.019822 


29 


132.00 


697.01 


7.58 


1142.9 


2.102890 


2.120574 


30 


166.43 


878.80 


6.01 


1817.2 


2.002182 


2.221232 


31 


209.85 


1108.0 


4.77 


2888.0 


1.901476 


2.321909 


32 


264.68 


1397.6 


3.78 


4595.5 


1.800768 


2.422721 


33 


333.68 


1760.2 


3.00 


7302.0 


1.700060 


2.623330 


34 


420.87 


2222.2 


2.38 


11627. 


1.599364 


2.624148 


35 


530.60 


2801.8 


1.88 


18440. 


1.498646 


2.724767 


36 


669.00 


3532.5 


1.50 


29352. 


1.397940 


2.825426 


37 


843.46 


4453.0 


1.19 


46600. 


1.297234 


2.926064 


38 


1064.0 


5618.0 


.96 


74240. 


1.196626 


3.026942 


89 


1341.2 


7082.0 


.75 


118070. 


1.095820 


3.127494 


40 


1691.1 


8930.0 


.69 


187700. 


0.995112 


3.228169 



* Calculated on the basis of Dr. Matthiessen 's standard, vis.: The 
sistance of a pure soft copper wire 1 meter long, having a weight of 1 enxa^ 
.141729 International Ohm at 0" C. The purest alununum obtainable has a 
conductivity of over 63 per cent, but this gain in conductivity is at a greatly 
increased cost. 



STHANDED ALUMINUM WIRE. 



■ded lT»a«fce i ' pi '««f AlaatlBBii Wire. 

(Triple Bimid.) 



udB. AS. 


^^sr 


\^% 


SsM w-sr 


VSSb's: 














































































































































231 





wof 



H. W. Bock. 

Betelin CoDdactiTitr ■2%. 

Rautance per Hil-f<w( lO.SS ohmt 

TeccqMratare 76* F, 

BmMic Limit 14.000 lbs. per sQiure in 

Dtlimkta Strencth 20,000 Iba. per iquue in 



I 



M 
it 

n 

a 

a 



MU 

ly 



li 



I 



!« 



I 



H 



.-; 



ill 



ll Sasis sSisS SSiSi siiis 

°» SKsSo 53*»3 SSSSa 2S_,2"' 






.T -" , ,"""."1P ^''l^ , . **. . .*^''! T*^ , . . 



IBON AND STEEL WIRB. 



199 



1. Struftded wire should alwavs be used, even in the smaller tises, as 
tbe action of the wind causes solid aluminum wire to "crvstallise," thereby 
its strangth; also, there is less liability of flaws in the metal 



camuiff trmtrngTi 

y» ^hr***!**""* gathers much less sleet than copper. 

8u It ooots less to string aluminum than copper, due to the less weight. 

4. Qve must be taken in stringing tflununum to prevent denting and 
abrasion, as the wire is very soft. 

5w Meefaanical and splice joints made without the use of solder are entirely 



6L Wires should be strung far enough apart to prevent trouble from 
barmng-off of the wire in case of a short eireuit. 

7. ^le to its high ooeffiei«it of linear expansion and low tensile strength, 
tba minimnm allowable sag for aluminum wire is considerably greater than 
for copper. This is one great objection to aluminum for telephone and 
telepapb Unea. For long spans the differenoe in deflection between alu- 
nattiim and oopper wires may be so great as to require a considerably higher 
pole in eaae aluminum is used, although the pole need not be as strong as 
would be required for copper^ as the weight of aluminum for equal oon- 
duetivity is but 47 per cent of the weight of oopper. 



C^aatoata of ]B«at CfalTaalaed Telegmpli 'VTire. 



Per eent Conductivity (copper 100) 

Per eent Conductivity (pure iron 100) 

teedfie Gravity 

Ibunds in 1 cubic foot 

n>andB in 1 cubic inch 

Founds per mile per circular mil 

Id* 

Ultimate strength, -. — 

sq. m. 

Modulus of elasticity,: — ^ — ^-4— 

m. X sq. in. 

Coefficient of linear Ejcpansion per ° C 

Coefficient of Linear Ebcpansion per * F 

Point in • C 

Point in **F 

\& Heat (watt-seconds to heat 1 lb. 1** C.) . 

Conductivity (watts through cu. in., 

temperature gradient 1* C.) 

Mtencf 

Maerohms per centimeter cube at 0" C. . . . 

IBerohms per inch cube at 0^ C 

Ohms per mil foot at'0° C 

Ohms per mil foot at 20^ C 

Ohms per mile at ** C 

Ohms per mfle at 20^ C 

Pounds per mi]eK>hm ^ C 

Pounds per mile-ohm 20° C 

Temperature (Toeffident per ** C 

Temperature Coefficient per *^ F^ 



Iron. 



16.8 
05.5 
7.8 
487 
.282 
.014 

66.000 

26.000.000 

.00012 

.000067 

1600 

2910 

200 

1.39 

9.5 

3.74 

67.2 

62.9 

302.000 

dr. mils 
832.000 

cir. mils 

4230 

4700 

.005 

.0028 



Steel. 



12.2 
09.2 
7.86 
480 
.284 
.0141 

68.000 

30.000.000 

.00012 

.000067 

1475 

2685 

209 

1.39 

13.1 
6.17 
78.9 
86.8 
417,000 



cir. mils 
458.000 

cir. mils 

5850 

6500 

.005 

.0028 



200 



PROPERTIES OP CONDUCTORS. 



IKradile Ctal' 



of ili« KUflieet Bl«ctric«l 4t«alUI 

ROBBLING. 






► 



4 
6 
8 
9 
10 

11 
12 
14 



8 


09 
-0 


•g 


c 


a 


o . 




in P 
Mile 


1 


eight 
per 


M 


730 


.225 


.192 


540 


.162 


380 


.148 


820 


.135 


260 


.120 


214 


.105 


165 


.080 


96 



I 



mile, 
mile, 
mile, 
mile, 
mile. 

Imile. 
mile, 
mile. 



Approximate 

Breaking Strain in 

Poundo. 



E.B.B. 


B.B. 


2.190 


2.409 


1.620 


1.782 


1.140 


1.254 


960 


1.056 


780 


858 


642 


706 


495 


545 


288 817 



Steel. 



2.701 
1,998 
1.406 
1,184 
962 

792 
611 
355 



Ayerage Reaistaaoe 
in Ohma at 68'* F. 



E.B.B. 


B3. 


6.44 


7.53 


8.70 


10.19 


12.87 


14.47 


14.69 


17.19 


18.08 


21.15 


21.96 


25.70 


28.48 


33.33 


48.96 


57.29 



Steel. 



8.90 
12.04 
17.10 
20.31 
25.00 

30.37 
39.39 
67.71 



The values given in this table are averages of a larse number of tests. 
They are withm the limits of the specifications of the Western Union Tele- 
graph Company. 

The average value of the mile-ohm is 4,700 for E. B. B. wire. 

The average value of the mile-ohm is 5.500 for B. B. wire. 

The average value of the mileK)hm is 6,500 for Steel wire. 

The average breaking strain is 3 times the weight per mile for E.B.B. 
wire. 

The average breaking strain is 3.3 times the woght per mile for B. B. wire. 

The average breaking strain is 3.7 times the weight per mUe for Steel wire. 

The mile^m — weight per mile X resistance per mile. 

Ctelrawlsed SigrBAl Stnuid. Sotmi fTirea. 



Diameter. 


Weight per 1000'. 


EMmated 
Breaking 
Weight. 


Inches. 


Bare Strand. 


Double Braid 
W. P. 


Triple Braid 
W.P, 


1-2 
15-32 
7-16 
&-8 
5-16 

9-32 
17-64 
1-A 
7-32 
8-16 

11-64 
9-64 
1-8 
3-32 


520 
420 
360 
290 
210 

160 

120 

100 

80 

60 

43 
33 
24 
20 


616 
510 
444 
362 
270 

214 
171 
148 
122 
96 

76 
60 
48 
38 


677 
561 
488 
398 
297 

235 
188 
163 
134 
105 

84 
66 
53 

42 


8.320 
6.720 
6.720 
4.640 
3.360 

2.560 
1.920 
1.600 
1.280 
960 

688 
528 
884 
320 



IBON AND STEEL WIRE. 



201 



• of Steel ITire. 

ROBBLINO. 

NoTB. — The breaking weights given for Heel win are not thoee of 5fael 
Tdtgraph wire. Thev appl^ to wire with a tensile strength of 100,000 
per square inch. This strength is higher than that oxtelegraph wire. 



No.. 
Roeb- 
iingO. 



6-0 
5^ 
4-0 
3-0 
^-0 



1 
2 
3 

4 

5 
6 

7 
8 
9 

10 
11 
12 
13 
14 

15 
16 
17 
18 
19 

30 
21 
22 
23 
24 

25 
28 
27 



80 
31 
32 
33 
84 

35 



Diam- 
eter in 



.460 
.430 
.893 
.362 
.831 

.307 



.263 
.244 
.225 

.207 
.192 
.177 
.162 
.148 

.135 
.120 
.105 
.092 
.080 

.072 
.063 
.064 
.047 
.041 

.035 
.032 
.028 
.025 
.023 

.020 
.018 
.017 
.016 
.015 

.014 

.0135 

.013 

.011 

.010 

.0095 
.009 



Area in 
Square 
Inches. 



.166191 
.145221 
.121304 
.102922 
.086049 

.074023 
.062002 
.054325 
.046760 
.039761 

.033654 
.028953 
.024606 
.020612 
.017203 

.014314 
.011310 
.008659 
.006648 
.005027 

.004071 
.003117 
.002200 
.001735 
.001320 

.000962 
.000604 
.000616 
.000491 
.000415 

.000314 
.000254 
.000227 
.000201 
.000177 

.000154 
.000143 
.000133 
.000095 
.000079 

.000071 
.000064 



Breaking 

Strain 

100.000 lbs. 

aq. inch. 



16.619 
14.522 
12.130 
10.292 
8,605 

7.402 
6.200 
5,433 
4.676 
3,976 

8.365 
2.895 
2.461 
2.061 
1.720 

1.431 

1.131 
866 
665 
503 

407 
312 
229 
174 
132 

96 
80 
62 
49 
42 

31 
25 
23 
20 
18 

15 

14 

13 
9.5 
7.9 

7.1 
6.4 



Weight in Pounds. 



Per 
1.000 ft. 



558.4 
487.9 
407.6 
345.8 
289.1 

248.7 
211.4 
182.5 
157.1 
133.6 

113.1 
97.3 
82.7 
69.3 
57.8 

48.1 
38.0 
29.1 
22.3 
16.9 

13 7 

10.5 
7.70 
5.83 
4.44 

3.23 
2.70 
2.07 
1.65 
1.40 

1.06 
.855 
.763 
.676 
.594 

.617 
.481 
.446 
.319 
.264 

.238 
.214 



Per Mile. 



2.948 
2.576 
2.152 
1.826 
1.627 

1.313 
1.116 

964 

830 

705 

597 
514 
437 
366 
306 

254 
201 
164 
118 
89.2 

72.2 
66.3 
40.6 
30.8 
23.4 

17.1 
14.3 
10.9 
8.71 
7.37 

6.68 
4.51 
4.03 
3.57 
3.14 

2.73 
2.54 
2.36 
1.69 
1.39 

1.26 
1.13 



Feet in 
2,000 lbs. 



3.682 
4.099 
4.907 
. 5.783 
6.917 

8.041 

9.463 

10.957 

12.730 

14.970 

17,687 
20.669 
24.101 
28.878 
34.600 

41.584 
62,631 
68.762 
89.525 
118,413 

146.198 
191.022 
259.909 
843.112 
450.856 

618.620 
740.193 
966,651 



This table was calculated on a basis of 483.84 pounds per cubic foot for 

ed wire. Iron wire is a tri6e lighter. 

The breaking strains are calculated for 100.000 pounds per square inch 
tbran^iout, simply for convenience, so that the breaking strains of wires 
of aaj strength per square inch may be quickly determined by multiplying 
the values given in the tables by the ratio between the strength per square 
inch and Iw.OOO. Thus, a No. 16 wire, with a strenirth per square inch of 

150.000 pounds, has a breaking strain of 407 X \^^ - ^10.6 pounds. 

The "Roebling" or "Maricet wire Gauge" is now' used as standard for 
ated wires in America. 



202 



PROPERTIES OP CONDUCTORS. 



lUBSMATAlfCS W^JLIIEA. 

SPKcmo Rbsistanck and Tempbratube CoBrFiciBirr. 



Substance. 



Platinum Bilver 

(Pt 66. Am 33) 
Patent-Niokel 

(Cu74.41. Zn0.23.Ni26.10.Fe0.42. 

Mn0.18) 

Platinoid 

(Cu 50 Zn 25.5, Ni 14, W 56) 
German Silver 

(Cu, Zn, Ni in various proportions) 
MaDganin 

(Cu, Ni, and Fe-Mn in varioiis propor- 
tions) 

Boker A Co.'s lala, hard 

Boker & Co.'s lala, soft 

Krupp's metal 

Driver-Harris 0o.'8 "as." 

Driver-Harris Co.'s "Advance" . . . . 
Driver-Harris Co.'8*'Ferro-Nickel" . . 
Constantin 



Microhms 

oer Cubic 

(Centimeter 

about 

20*F. 



31.726 

34.2 
32.5 
10 to 46 



42 to 74 

50.2 

47.1 

85.18 

55.8 

48.8 

28.3 

50 to 52 



Temperature Coeffi- 
cient per ** 0. 



.000248 
.00019 



.00025 to .00044 



.000011 to .00014 
—.000011 
+.000005 
.0007007 
Small 
Very small 
.00207 



««] 



Silver. 



German silver is an alloy of copper, nickel, and lino. The eleotrioal 
properties of the alloy naturally vary considerably with the proportions of 
the constituent metals. The proportion of nidcd present is ordinarily used 
to distin^^uish the various alloys, as the amount of this metal jpreeent in the 
alloy fixes the proportions of tne other constituents in order that the result- 
ing material may be easily worked. As made in the United States, com- 
mercial German silver is made with approximately the following propor- 
tions. 

(Dr. F. a. C. Perrine.) 



Designation. 


0>nstituents. 


Resistance at ** C. 


Per Cent. 
Alloy. 


Nickel. 


Copper. 


Zinc. 


Microhms 
Per Centi- 
meter. 


Ohms 

Per Mil 

Foot. 


8 

12.5 
20 
30 


8 

12.5 
20 
30 


60 
67 
66 
60 


32 
30.5 
24 
20 


19 
26 
32 
46 


114 
160 
193 
277 



Specific gravity, 8.5. 

Temperature toeffident per <» C, .00025 to .00044. 



GERMAN SILVER WIRES. 



203 



•f «• 



•Uvcr fl^ire. 





1»% 


a©% 


81m. 










B.dES. 


Ohnuper 
1.000 fW. 


Ohms per 
Pound. 


0hmsj;>6r 
1.000 Feet. 


Ohms per 
Pound. 


No. 8 


11.7 


.235 


17.6 


.363 


9 


11.8 


.374 


17.7 


.662 


10 


18.7 


.696 


28.0 


•o94 


11 


23.5 


.948 


85.3 


1.42 


12 


29.7 


1.50 


44.6 


2.26 


13 


87.6 


2.39 


56.2 


3.59 


14 


47.3 


3.81 


70.9 


5.71 


15 


69.6 


6.06 


89.4 


9.09 


16 


75.2 


9.63 


112. 


14.4 


17 


94.8 


15.3 


142. 


22.9 


18 


119. 


24.3 


179. 


36.5 


19 


166. 


40.9 


232. 


61.4 


20 


190. 


61.6 


285. 


92.4 


21 


239. 


97.9 


359. 


146. 


22 


302. 


155. 


453. 


233. 


23 


381. 


247. 


671. 


371. 


24 


480. 


393. 


721.. 


690. 


26 


606. 


626. 


900. 


939. 


26 


764. 


995. 


114. 


149. 


27 


964. 


158. 


144. 


237. 


28 


121. 


261. 


182. 


377. 


20 


153. 


400. 


229. 


600. 


30 


193. 


636. 


289. 


955. 


31 


243. 


101. 


366. 


151. 


32 


307. 


160. 


461. 


241. 


88 


387. 


255 


581. 


383. 


84 


488. 


407. 


733. 


610. 


36 


616. 


647. 


924. 


970. 


36 


777. 


102. 


116. 


154. 


37 


979. 


163. 


146. 


245. 


88 


123. 


257. 


185. 


386. 


39 


156. 


409. 


233. 


614. 


40 


196. 


652. 


294. 


978. 



Db. F. a. C, Perrinb. 

Perfaaiw the meet remarkable remstance alloy which has been produced 
is manganin. invented by Edward Weston in 1889. It is composed of 
co^cr, niekd, and ferro-manganese in varying proportions. 

fTci. Nichols of Cornell, has shown that coils made of this material 
sre spt to chance their resistance when successively heated to 100*^ Cent. 
^ cooled toO**Cent.. but Dr. lindeck, working for the Reichsanstalt. states 
that when a completed coil is aimealed at a temperature of 140^ Cent, for 
vn boors, no finlher difficulty is experienced from any aging change, 
*l^ha> produced by time or repeated heatings and coolings. 
^A fortner advantage of man^^anin which has been noticea by Dr. Lindeck, 
*wa used for resistance coils, is its very feeble thermo-electnc power when 
y»q <PBd to copper, as is almost idways the case in standard coils. While 
lor german sinner the thermo-electric power is between 20 and 30 micro- 
voHa par degree Centigrade, and for oonstantin, an alloy of copper 50 parts 
^^M^mekel 60 parts, having a temperature coefficient between .00003 and 
•OCODl a thermo-electric power of 40 micro-volts per degree Centigrade is 
"Old. the thermo-^eetrio power of manganin is not above one or two mioro- 
^ws par degree. 



( 



204 



PROPERTIES OP CONDUCTORS. 



■lectrlcal P^pertt< 



«• AMd COIUltltllMOM of IHtftBVABftM* 

Dr. F. A. C. Perrxne. 







1 




Mi- 






Composition. 


Ohms 


crohms 


Temper- 
ature Co- 
efficient* 


Authority. 






per 
Mil- 


Cubic 










Cu. 


Fe. Mn. 


Ni. 


Foot. 


Centi- 












meter. 




Nichols 


78.28 


14.07 


7.65 


• • • 




0.000011 


Nichols 


51.52 


31.27 


16.22 


• p • 


• • • • • 


0.000039 


Perrine 


70. 


25. 


5. ) J, 4) 


392 


65.15 




Perrine 


65. 


30. 


s-lli 


404 


67.2 




Perrine 


65. 


30. 


6.)S5 


443 


73.6 




Feussner and Lindeck 


73. 


24. 


3. 


287 


47.7 


0.00003 


Lindeck 


84. 


12. 


4. 


253 


42.0 


0.00014 


Dewar and Fleming . 


84. 


12. 


4. 


287 


47.64 


0.0000 



leitaiona, Realatttnco, and Weicltta of 

BoKER A Co.'s IaIa. 



RosUtanco 11^1 



I 



Specific gravity 8.4 

Microhms per centimeter cube, 0^ C, hard 50.2 

Microhms per centimeter cube, 0° C, soft 47 . 1 

Microhms per mil-foot, 0^ C, hard 3.10 

Microhms per mU-foot, 0° C, soft 28.4 

Temperature co^&cient per 0° C, hard . — .000011 

Temperature coefficient per 0° C, soft + .000005 













Carrying 


B. &. S. 

Gauge 

No. 


Diameter, 
Inch. 


Area, 

Circular, 
Mils. 


Ohms per 
1000 Feet. 


Feet per Lb. 
Approxi- 
mately. 


Capacity 
with Free 
Radiation 
Amperes. 


14 


.0641 


4107. 


73.5 


86. 


■ • • • 


16 


.0508 


2583. 


116.9 


135.3 


• ■ • ■ 


17 


.0453 


2048. 


147.4 


170.6 


• • ■ • 


18 


.0403 


1624. 


185.9 


215.5 


15.8 


19 


.0359 


1289. 


234.3 


271.0 


13.6 


20 


.0320 


1024. 


295.6 


842.3 


11.5 


21 


.0285 


812.3 


374.4 


433. 


9.7 


22 


.0253 


640.1 


470.1 


543.5 


8.0 


23 


.0225 


506.25 


596.6 


689.6 


6.8 


24 


.0201 


404. 


747.6 


870. 


5.8 


25 


.0179 


320.4 


945.6 


1098. 


.4.9 


26 


.0169 


252.8 


1192.9 


1370. 


4.1 


27 


.0142 


201.6 


1497.8 


1724. 


3.6 


28 


.0126 


158.8 


1890.1 


2174. 


3.1 


29 


.0113 


127.7 


2407.8 


2777. 


2.9 


30 


.0100 


100. 


3005.3 


3448. 


2.7 


31 


.0089 


79.2 


3789.2 


4347. 


• • • ■ 


32 


.0080 


64. 


4779.1 


5555. 


2.5 


33 


.0071 


50.4 


6025.1 


7142. 


■ • « • 


34 


.0063 


39.69 


7600.4 


9090. 


2.2 


35 


.0056 


31.56 


9582.7 


11100. 


• a • • 


36 


.005 


25. 


12081. 


14286. 


2.0 


37 


.0044 


19.83 


15229. 


17543. 


.... 


38 


.004 


16. 


19213. 


22220. 


a . . . 


39 


.0035 


12.25 


24218. 


27700. 


.... 


40 


.0031 


9.61 


30570. 


35714. 


• . . • 



Supplied by Boker Co.. 101-103 Duane St., New York. 



boker's resistance ribbon. 



205 



I» K« <^wai«7. 



• 


S4 


Ohms per 1000 feet. 


ni 

o 


iin. 


1 in. 


fin. 


i in. 


1 in. 


|in. 


iin. 


1 in. 


8 


.128 

1 


14.81 


7.40 


4.93 


3.70 


2.96 


2.46 


2.11 


1.85 


9 


.114 


16.69 


8.34 


5.56 


4.17 


3.34 


2.78 


2.38 


2.08 


10 


.101 


18.80 


9.40 


6.26 


4.70 


3.76 


3.13 


2.70 


2.35 


11 


.0907 


20.97 


10.48 


6.99 


5.24 


4.19 


3.49 


2.99 


2.62 


12 


.0808 


23.46 


11.73 


7.82 


5.86 


4.69 


3.91 


3.35 


2.93 


13 


.0719 


28.63 


13.31 


8.87 


6.65 


5.32 


4.43 


3.80 


3.32 


14 


.0641 


29.62 


14.81 


9.87 


7.40 


5.92 


4.93 


4.22 


3.70 


15 


.0571 


33.38 


16.69 


11.12 


8.34 


6.68 


5.56 


4.77 


4.17 


16 


.0508 


37.60 


18.80 


12.53 


9.40 


7.52 


6.26 


6.37 


4.70 


17 


.0452 


41.94 


20.97 


13.98 


10.48 


8.38 


6.99 


5.99 


5.24 


18 


.0408 


46.02 


23.46 


15.64 


11.73 


9.38 


7.82 


6.70 


5.86 


19 


.0359 


53.26 


26.63 


17.78 


13.31 


10.64 


8.87 


7.60 


6.65 


20 


.0320 


59.24 


29.62 


19.75 


14.81 


11.84 


9.87 


8.46 


7.40 


21 


.0284 


66.76 


33.38 


22.25 


16.69 


13.35 


11.12 


9.53 


8.34 


22 


.0253 


75.20 


37.60 


25.07 


18.80 


15.04 


12.53 


10.74 


9.40 


23 


.0225 


83.88 


41.04 


27.96 


20.97 


16.77 


13.98 


11.96 


10.48 


24 


.0201 


93.84 


46.92 


31.28 


23.46 


18.77 


15.64 


13.40 


11.73 


25 


.0179 


106.52 


53.26 


35.50 


26.63 


21.30 


17.78 


15.21 


13.31 


26 


.0159 


118.48 


59.24 


39.49 


29.62 


23.69 


19.75 


16.01 


14.81 


27 


.0142 


133.52 


66.76 


44.50 


33.38 


26.70 


22.25 


19.07 


16.69 


28 


.0128 


150.40 


75.20 


50.13 


37.60 


30.08 


25.07 


21.50 


18.80 


29 


.0112 


167.76 


83.88 


55.92 


41.04 


33.55 


27.96 


23.96 


20.97 


30 


.0100 


187.68 


93.84 


62.56 


46.92 


37.53 


31.28 


26.81 


23.46 


31 


.0089 


213.04 


106.52 


71.01 


53.26 


42.60 


35.50 


30.43 


26.63 


32 


.0079 


236.96 


118.48 


78.98 


59.24 


47,40 


39.49 


33.82 


29.62 


33 


.0071 


267.04 


133.52 


89.01 


66.76 


63.40 


44.50 


38.15 


33.38 


34 


.0063 


300.80 


150.40 


100.26 


75.20 


60.16 


50.13 


42.97 


37.60 


35 


.0056 


335.52 


167.76 


111.84 


83.88 


67.10 


55.92 


47.93 


41.94 


38 


.005 


375.36 


187.68 


125.12 


93.84 


75.07 


62.56 


53.62 


46.92 


87 


.0044 


426.06 


213.04 


142.02 


106.52 


85.21 


71.01 


60.87 


53.26 


38 


.004 


473.92 


236.96 


157.97 


118.48 


94.78 


78.98 


67.64 


59.24 



206 



PROPERTIES OP CONDUCTOR0. 



Specifie sravity 8.102. 

Specific resistance at 20^ C. mean 85.18 mierohins. 

Temperature coefficient, mean 0007007. 

Resiatance per circular mil-foot 314. ohms. 

Resistance per lOOO', 1 square inch area . . . .8613 ohms. 

This metal can be permanently loaded with current sufficient to raise its 
temperature to 600^ C. (1112^ F.) without undergoing any structural chan^ 
It should never be put in contact with asbestos, however, as this matensl 
oauses it to deteriorate rapidly* 



Diam. 


Diam. 
in Inches. 


Keai^ 
est 

B.&S. 
Gauge 


Feet 


Resistance In ohms per foot. 


In m.m. 


at 


at 


at 


at 






No. 




68° F. 


1760 F. 


2840F. 


4280 F. 


6 


.1968 


4 


9 


.0132 


.0138 


.0143 


MBO 


4 


.1772 


6 


12 


X)163 


.0170 


Mie 


.0184 


4 


.1576 


6 


15 


.0206 


.0216 


.0224 


M36 


H 


.1378 


7 


19 


.0209 


.0280 


.0291 


.0907 


3 


.1181 


2+ 


26 


.0368 


.0382 


.0896 


J0417 


21 


.1063 


9- 


31 


.M37 


.0456 


.0472 


JM/n 


P 


.0864 


10 


37 


.0628 


JOBBO 


.0670 


Mtn 


.0686 


11 


46 


.0663 


.0679 


.0706 


.0742 


2 


J0787 


12 


68 


.0826 


.0860 


J0892 


M¥} 


If 


.0688 


13 


76 


.1078 


.112 


.116 


.123 


1} 


.0600 


16 


104 


.1468 


.163 


.169 


.107 


1| 


jM92 


16 


160 


.2116 


.220 


.229 


.241 


1 


.0383 


18 


234 


.3306 


.344 


.366 


.376 


J 


01296 


21 


416 


.6870 


.610 


.633 


.067 


.0196 


24 


937 


1.324 


1.38 


1.43 


IJil 



American Agent, Thomas Prosser A Son, 15 Gold St., New York C^ty. 



-wi 



Hside bj DrlTer-^Uurrla IFire Co. 
HsMTviaoM, If. jr. 



•*B. B." — Resistance per mil-foot at 76" F. 

Low temperature coefficient and low thermo-eleotrie effect 
against copper. Will not rust. 

"AuVANCB." — Resistance per mil-foot at 76** F. 

A copper-nickel alloy containing no sine. Temperature 
coefficient practically nil. 

•*F«RRO-NicKEL." — Resistance per mil-foot at 76* F. 
Temperature coefficient per ^ F. 

About the same resistance as German Silver, but weighs 
about ten per cent less and is cheaper. 



830 ohms 



204 ohms 



170 ohms 
.00116 



DRIVER-HARRIS RESISTANCE WIRES. 



207 



vf l»rlY«r»Hw 



: 


"S. B." 


"Advance." 


••Ferro-Nickol." 


No. B. A & 










Ohma per 
1.000 ft. 


Ohmsp^r 
1.000 ft. 


Ohms per 
1,000 ft. 


10 


82 


28. 


2.0 


11 


40 


35.5 


2.5 


12 


51 


44.8 


3.2 


13 


64 


56.7 


4.1 


U 


82 


71.7 


5.1 


15 


103 


90.4 


6.5 


10 


130 


113 


8.2 


17 


168 


145 


10.4 


18 


210 


184 


13.1 


19 


260 


.226 


16.3 


20 


328 


287 


20.5 


21 


415 


362 


25.9 


22 


526 


460 


32.7 


23 


600 


575 


41.5 


24 


831 


726 


52.3 


26 


1.060 


010 


65.4 


26 


1.828 


1.162 


85 


27 


1.667 


1.455 


106 


28 


2.112 


1,850 


131 


29 


2,625 


2.300 


166 


30 


3.360 


2.940 


209 


31 


4,250 


3.680 


266 


32 


5.250 


4.600 


333 


33 


6.660 


5.83a 


425 


34 


8,400 


7,400 


531 


35 


10.700 


9,360 


672 


36 


13.440 


11.760 


850 


37 


16.640 


14,550 


1,070 


38 


21,000 


18.375 


1,330 


39 


27.540 


24.100 


1.700 


40 


37,300 


32.660 


2.120 


■ • 


• • • 


. • « 


. • • 



208 PROPERTIES OF CONDUCTORS. 



oiTMmmx cAS]ftiniv« cajpaoktit ojt 

A]ffl» GAllIiKII. 

Let Z> "■ dimmeter of wire or cable core in inches. 

T — temperature elevation of wire or cable core in * Centigrade. 
/ — current in wire in amperes. 

r ■■ apecifio resistance of wire in ohms per mil-foot at final tena- 
perature. 

The following ^>proximate formula give results sufficiently accurate for 
practical purposes. 

Bare Owrhead Wzrks Out of Doobs. 
Stranded : Solid : 

Barb Wues In Doors, Expobbd. 
Stranded : Solid : 



/ « 610 



y Z:^. / - 060 y/I^. 



SxNOLB Conductor Rubber Coybrbd Cable in Snix Air. 
Stranded : Solid j 



ijei iwin iTiia * a^^s&^A 

/ - 490 y^. / - 530 y ^ 



SiNaLB Conductor Rubber Covbrbd Lead Sheathed Cable im 
Underground Single Duct Conduit. 

Stranded : Solid : 

/ - 490 y^. / - 530 ^I^. 

SiNOLE Conductor Paper Covered Lead Sheathed Cable in 
Underground Single Duct Conduit. 

Stranded : Solid : 

/ - 430 y^. / - 470 ^T^. 

* Three-Conductor Rubber Covered Lead Sbeathbd Cable in 
Underground Single Duct Conduit. 



Stranded : 


Solid: 


/ - 370 i/^^- 
^ r 


7-4O0v/^^. 


* Three-Conductor Paper Covered Lead Sheathbd Carle in 
Underground Single Duct Conduit. 


Stranded : 


Solid: 


/-320\/^^. 


7-350 y/^^. 



* / is here current per wire. 



CAPACITY or WIRES AND CABLES. 



NinoHAi. ELBcniiciL Codb. 



V'^ 


c^ 


^ 


¥ 


^^ 


W 


"a^ 








AmpanuL 


AiDptna. 






















































































































































































































211,800 


210 


312 




l.OIO 


ii 

,870 



< 



idetf 0*p|Mr CtmdBt 





Natiohu, Ei-ectbical 


CODt 






B,4&C. 


n.'E"' 


No. of 

StlSBdlU 


«s!"ii:'^ 


Ampffo. 


■■■ 111 


1.28S 








18 


.1 










B 










i? 










21 










SS 




".338 




































60 










60 




«igT 




















73:778 










99,064 






120 




124,628 






145 




is7%ea 






170 




198,877 
















235 


























127 







m win Uie c&rryiajf capainty of any fii 
of the TBlot giTBD tn the sbon table. 



SIM is to be takso 



r 



210 



PBOPERTIES OF GONDUCTOBS. 



Carrjlair C a p a ci ty of 1 

{From Uehnieal letter of Oeneral Electric Company.) 



The following table of earrjring capacity ia baaed on teste of cables in 
■till air. Insulation alone A' thick; lead A' to f thick; jute and 
asphalt jacket A' thick. Pap«r insulated cables heat S% to 10% more 
than rubber insulated cables with same current and thickness of ooverixiga. 
Cables require about four hours to reach final temperature. 



60% of total increase in temperature in Ist hour. 

30% of total increase in temperature in 2d hour. 

8% of total increase in tenq>erature in 3d hour. 

Cables immersed in water will carry 60% more current with same inc 
of temperature, and cables buried in moiet earth about 15% more. Rubber 
cables should not be run above 70^ C. Paper cables should not be run aboTS 
90* C. 



) 







Amperes at 30"* C 


Amperes at 50^ C 




Diameter 


Bise. 


Rise. 




Copper 

Core. 

Inches. 










Bise. 














Leaded 




Leaded 




Braided. 


and Jute 


Braided. 


and Jute 








Covered. 




Covered. 


6 B. dc & Aolid 


.162 


61 


56 


76 


68 


4 B. & S. Solid 


.204 


85 


78 


104 


94 


2 B. & 8. Stranded 


.300 


133 


121 


162 


146 


1 B. A S. Stranded 


.325 


155 


141 


189 


'170 


B. 4c S. Stranded 


.390 


191 


174 


231 


210 


00 B. & S. Stranded 


.420 


218 


199 


268 


241 


000 B. ft a Stranded 


.476 


266 


242 


326 


283 


0000 B. ft S. Stranded 


.543 


320 


291 


891 


352 


250000 CM. 


.570 


355 


824 


435 


892 


300000 CM. 


.640 


414 


877 


506 


456 


350000 CM. 


.680 


460 


419 


568 


607 


400000 CM. 


.735 


512 


466 


626 


564 


450000 CM. 


.787 


562 


511 


687 


618 


500000 CM. 


.820 


606 


551 


742 


668 


600000 CM. 


.900 


604 


631 


848 


763 


750000 CM. 


1.020 


825 


760 


1016 


915 


900000 CM. 


1.096 


940 


855 


1149 


1034 


1000000 CM. 


1.157 


1017 


925 


1338 


1200 


1250000 CM. 


1.298 


1204 


1095 


1481 


1328 


1600000 CM. 


1.413 


1376 


1251 


1644 


1480 


2000000 CM. 


1.760 


1766 


1606 


2178 


1960 



HeaiiBC of Cable* la Maltlpla l»ac« Caadait. 

The mutual heatins of cables in multiple duct conduit has been hum' 
tigated experimentally by H. W. Fisher. The following diagram sad 
table shows the arrangement of the conduit system used by him and the 
size and kind of cable in each duct. Means were provided for copnectiog 
any or all the cables in series and observing the temperature of the eeiw 
doctor in each duct. 



CAPACmr OF WIRES AND CABUBS. 



211 



© ® ® 


© 


© © ® 


© 


© © 


® 



Fio. 22. 





Number of 


Sise B. A B. and 




Cable. 


ConduotorB. 


CM. 


Insulation. 


A* 




000 


Jf' and ^' Paper 


B 


1 


600.000 


X' Paper 


0> 




000 


X" and A' Paper 


D 




500.000 


X' Paper 


E 




1.260.000 


jC' Paper 


F 




1,260.000 


X' Paper 


G 




000 


j^' Paper 


H 




000 


Rubber 


I 




1.260.000 


A'Papw 
A' Paper 


J 




1.260.000 


K 




000 


Rubber 


L 




000 


A' Paper 



* The three conductors of A and C in multiple. 



Fisher's restilte are summarised in the following table : 



E,F.I,J. 



Conductors 
Canying Current. 

G, H, K, L.. ••■•••■ 



A, B, C, V, £, Ff If J. ... 



SO*" C. Rise. 



Conductor. 



A.AC. 
(G 

L 

I 

E 

J 

F 

B 

D 



(J 

\ 



Amperes. 



130 
155 
180 
600 
690 
560 
636 
355 
400 



60« C. Rise. 



Conductor. Amperes, 



A.AC. 
G 
L 
I 
E 
J 
F 
B 
D 



180 
190 
260 
766 
760 
725 
690 
425 
550 



An tnq>ectk>n of this table will show that the current corresponding to a 
nwtn temperature elevation is in each case less than that given by the 
lormulaB on page 206. the difference bein^ from 4 to 26 per cent, depend- 

>t conductors in service and the location of the cable 



the number oi . . . 

in question. It is to be noted that comer ducts radiate heat the best, and 
■U outside ducts radiate heat much better than do the inside ducts. 



r 



212 



PROPERTIES OP CONDUCTORS. 



per Voot 'Ei9mt Im ftiBirl«*CJoM«l«ctor C«1»le« »« 
IHIIereat MAxtmvm TeBftp«ratiir« wltli IMIi«reM« 

Amouito or 4 



(From Handbook No. XVII, 1906. Copyrighted by Standard Under- 
ground Cable Company.) 



• 

Sise B. A S. 




Current in 








6 


66 


81 


93 


104 


114 


123 


5 


74 


91 


106 


117 


128 


138 


4 


84 


102 


117 


131 


144 


153 


3 


93 


114 


132 


148 


161 


175 


a 


106 


128 


148 


186 


181 


196 


1 


118 


148 


166 


186 


203 


220 





132 


162 


187 


209 


228 


247 


00 


149 


181 


210 


235 


256 


277 


000 


166 


204 


235 


263 


288 


311 


0000 


186 


229 


264 


'298 


828 


260 


Area in 














1000 C. M. 














300 


222 


273 


315 


352 


385 


416 


400 


248 


316 


363 


406 


445 


480 


600 


288 


352 


406 


456 


498 


537 


000 


315 


385 


445 


497 


646 


587 


TOO 


841 


416 


480 


688 


688 


6S6 


800 


364 


446 


514 


676 


628 


679 


000 


386 


473 


545 


610 


666 


720 


1000 


407 


498 


575 


642 


703 


758 


1100 


426 


522 


602 


674 


736 


796 


1100 


446 


846 


630 


706 


772 


8SS 


1300 


462 


668 


655 


732 


802 


866 


1400 


480 


590 


681 


761 


834 


90O 


1500 


496 


610 


704 


788 


862 


931 


1600 


512 


629 


726 


812 


889 


960 


1700 


629 


649 


780 


887 


916 


990 


1800 


543 


667 


770 


862 


943 


1018 


1900 


557 


686 


792 


886 


970 


1048 


2000 


573 


705 


813 


910 


995 


1075 








Watts lot 


it per ft. 






Temp. (100 


1.81 


2.71 


3.62 


4.52 


6.43 


6.33 


of oond. 128 


1.91 


2.87 


8.82 


4.78 


6.78 


6.69 


in«F. 160 


2.00 


3.00 


4.00 


6.00 


6.00 


7,00 



The watts lost per foot means the amount of electric energy lost in heat- 
ing the conductor and is equal to the product of the resistance per foot of 
cable times the square of the current in amp>eres. 

The above table is useful in showing the watts lost in heating effect per 
foot of cable with dififerent currents, and also in finding the sue of con- 
ductor that must be used for a given current and watts per foot loss. 

for Two-Condactor Cables the watts corresponding to the dif- 
ferent currents must be multiplied by two, and to obtain the currents 
corresponding to the watts in the table multiply the currraits given in the 
table by .707. 

for Vhree-Conductor Cal»Iea the watts corresponding to the 
currents in the table, must be multiplied by 3. and to obtain the currents 
corresponding to the watts in the table multiply the currents given in ike 
table by .577. 



CAPACITY OF WIRES AND CABLES. 



213 



€;«iv«Mt CanyiaiT Capacity mt 



C«T«re4 CaMes. 



(Fiom Handbook No. XVII. 1900. Gopyrighted by Standard Under- 
ground Gabla Company.) 

The eurrcnt carrying cai)acity of insulated copper oablei sheathed with 
lead depends primarily upon 

(a) The sise and number of oonductonti and their relative position. 

(&) The ability of the insulating material to withstand high tempera- 
tnras and to conduct heat away from the copper conductor, — this latter 
being in turn dependent upon kmd of insulation and its thickness. 

(e) The initial temperature of the medium surrounding the cable. 

la) The ability of the medium surrounding the cable to dissipate heat 
with small temperature rise. 

(e) The number of operating cables in dose proximity and their relative 



Where a number of insulated conductors are under the same sheath, 
they are subject to an interchange of heat somewhat similar to that which 
takes place when a number of separate cables are laid closely together, 
and for that reason each conductor of a multi-conductor cable will nave a 
smaller current carrying capacity than a singlensonductor cable. If the 
rariouB oonductora are separately insulated and laid to^^her in the form 
of flat or round duplex or triplex, thdr carrying capacity will be greater 
than if they are laid up in the form <^ two-conductor concentric or thre&- 
oonduetor concentric, since the enveloping conductors in the latter forma- 
tion seriously retard the dissipation of heat from the inner conductors. 
Assuming that unity (1.00^ represents the canying capacity of single- 
eonductor cables, the capacity of multi-conductor cables would be pven 
by the following: 



2 oond. flat or round form, 

3 eond. triplex form 



.87; concentric form, 
.75; concentric form. 



.79 
.60 



The following experiment on duplex concentric cable of 525,000 C. M. 
iadiestes clearlv the danger in subjecting this type of cable to heavy over- 
ioeds Of even snort duration. The cable was first heated up by a current 
cf 440 amperes for 5 hours. An overload oi 50 per cent was then applied, 
the resolts In degrees Fahrenheit above the surrounding air being as 
follows: 



Time from Start. 


OMin. 


15 Min. 


30 Min. 


45 Min. 


60 Min. 


90 Min. 


Inner Conductor 
Outer Conductor . 
LeadCover . . . 


70° 

55 

31 


84« 

65 

35 


98* 

76 

40 


111«» 
85 
45 


123* 
94 
49 


142« 
108 
57 



In any eaUe the area over which dissipation of heat must take place is 
proportional to the circumference of the conductor or (since the oircum- 
loenee varies as the diameter), upon the diameter of the conductor, while 
the croas section of the conductor varies as the sauare of the diameter. 
Hence the sise of conductor varies much more rapidly than its heat radiat- 
iac sm^iee, and in oonsSQuenoe the amperage per sauare inch, or circular 
inu of oopper seetion, must be less for large size oonauctors than for small, 
in order to have the same rise of temperature under the same conditions. 
Hie nsoal formula for carrying capacity. 



Current » 



(diam. of Cond.)* 
A constant 



aeoount of this fact but not to a sufficient degree, and we find that 

for caUes as ordinarily used in underground work, a more correct expression 
li the following: 

Current — (d"Mn. of Cond.)t 
A constant 



214 



PROPERTIES OF CONDUCTORS. 



Rubber iiuulation ia a somewhat better heat conduetor than dry or 
saturated paper, and therefore, when applied to the same siae eonduetor ia 
equal thickness, will permit of a larger current flowing in the conductor fer 
the same rise of temperature above the surrounding air. On the otbcrl 
hand, rubber deteriorates much more rapidly at high temperaturee thaa 
saturated paper, and while this disadvanta^ is apparently oompenaated 
for up to about 150^ Fahrenheit by its superior heat dissipating qualities, at 
higher temperatures deterioration takes place and becomes so serious tnat 
its value as an insulating medium disappears in a comparatively short tixncl 

As the thickness of insulation is increased, the temperature of the con-i 
ductor, with any given current flowing graaually, increases and tbereforei 
the current oarrsring capacity becomes reduced. The reduction in capacity 
however, is not very great, being in the ratio of about 03 for H instuation 
to 100 for A insulation, so that the values in the table given below ahould { 
be slightly cfecreased when greater thicknesses than A are used. 

As It is the final temperature reached which realiy affects the cajryincl 
capacity, the initial temperature of surrounding medium must be takeefi 
into account. If, for instance, the conduit system parallek steam or ha%\ 
water nuuns, the temperature of ISO** F. (which we have assumed in th«| 
table on page 215 to be the maximum for safe continuous work on cables] 
will be reached with lower values of current than would otherwise be 
case; and as 70^ is the actual temperature we have assumed to exist in 
surrounding medium prior to loading the cables, any increase over 
must be compensated tor by reducing the current carried. 

For rough calculations it will be safe to use the foUowing multiplicn to| 
reduce the current carrying capacity i^ven in the table on page 2lo to thej 
proper value for the corresponding mitial temperatures: 



Initial Temp. . 


70 


80 


90 


100 


110 


120 


130 


140 


150 


Multipliers . . 


1.00 


.83 


.86 


.78 


.70 


.60 


.48 


.34 


.00 



The ability of the surrounding medium to dissipate heat, directly affeets 
the carrying capacity of the caDles, as with the same current the cable 
might be comparatively cool tf laid in good heat conducting matoial such 
as water, and dangerously hot if laid in poor heat opnduol- 

O^^-^y^^ ing material such as dry sand. Ordinary conduit Bystema 
I of clay or terra cotta oucts laid in cement, dissipate heat 
^ J fairly wdl, the outside ductSL however, bemg much more 
OV-*'^^"~K^ efliaent in this function than the inner ones, so that an ideal 
I system, from this point of view, would consist of a single 
^ J horisontal layer of ducts. As this would require an enormoos 
O^^ • C width of trench and considerable inconvenience in handling 
I the cables in manholes when many cables are to be installeo. 
^ J we would suggest the form shown in Fig. 28 as being more 
O^^^^FTTTx practicable. 
T( ] I Where more ducts are required, the vertical section shown 
JC^J could be easily duplicatecLa considerable space, however, 
"^"^Ti^ being left between them. With this arrangement, the cany- 
Fig. 23. {Qg capacities given in the table on p. 215 could be somewhat 

increased. 
When a number of loaded cables are operating in dose proximity to one 
another, the heat from one radiates, or is carried by conduction, to each of 
the others, and all raised in temperature beyond ^„^^^ — ^ 
what would have resulted had only a single cable fVSY/^^Y/'^ 1/^^ 
been in operation; and if the cables occupy ll^lv^I^H^ 
adjacent ducts in a conduit system of approxi- S— A.i ^ ^ ( 
mately square cross section laid in the usual way, (/Ok | /TnT/^ T /^^ 
the centrally located cable or the one just above I V5/l VC/lL-zlw 
the center m large installations (A in Fig. 24) ^ ^ ^ ^ 
will reach the highest temperature. This is equiv- 
alent to saying that its carrying capacity is 
reduced, and while this reduction does not amount 
to more than about 12 per cent (as compared piQ. 24. 

with the cable most favorably located, — as at 

Z>, Pig. 24) in the duct arrangement given, it may easily assume much 
greater proportions where large numbers of cables are massed together. 



©MoTq 



CAPACITY OP WIBES AND CABLES. 



tatn b* Wed, lbs unncB nurriag npaeity mny M takce 
Kiir Hopv «H of oonduetor,' and for isbls of > clvai 
■nnruiK eapscitics of all abW evao thou^ plaoad ia M 
■ b* Rtnssiled by the following fisuna, takiiiB unity aj 
mpm avaty <d tour ablu: 



CwTwat CarcTJar 0>a«clH«» f»r Coble* 
a^ fTatU l.M« p«r Km. 

kvuM giogls eonduotor paper i-.iiT.ijH lead 



B> adi of four equally loadad giogle n 

^^ «^n tha initial tampentun do«g oot aiOMd 7U" tr„ ttae nuauaum 
■taBpantun for eontinuoui opsntion beioi takan at 1«)° F. 

Wm HandbDok No. XVII. lOOS. Copyri(h(ed by Studud TToder- 
fmund Cable Compaay.} 



as; 


Siw 


Ampwea. 


Watti* 

toot per 


.M. 


C. H. 


,£•¥. 


87 


300,000 


333 


4 32 




03 


400.000 








09 






.01 




IS 






,1S 




M 






.M 








e07 










650 


:7i 






.1 00' 


ess 


.88 






00 


710 


.01 






1,: 00 


TW 






3t 


. .: 00 


S90 


:25 




54 


00 


M7 


.37 








S95 


0.49 






'.■ 00 


033 






M 


t^ « 


•TO 


«:Tt 




40 


00 


toio 


.86 




OB 


.900,000 








99 


Z.000.000 


1085 


:o9 



at* Uia amount of oiersy whioh la traiuformed 
t be diMlpated. It ia wEst is usually called the 
lytulnctor/ tha DURcnt values Elvao: and for A 
<otiTe oooduotor at a temperature of 150° T. 
eompiled from a loni seriea of testa made by ua 
{lacan Falls Power Company, the sonduil system 
in Fig. 24. The dusla ware ol terra cotta with 



i 



216 



PROPERTIES OF CONDUCTORS. 



SecoHiHieadcd Power Cmwwjtmg Capaclt;^ 
of ItoUverMl fiaovjirj, Xltroo-ConAactor 

Calilos. 



Itr i» KllowaiJ 
, Throo-Pli«oo 1 



(From Handbook No. XVII. 1906. Copyrighted by Standftitl Under- 
ground Cable Company.) 



Sixe in 


Volts. 


B. & S. G. 


1100 


2200 


3300 


4000 


6600 1 


11000 


13200 1 


22000 




Kilowatts. 


6 


02 


183 


275 


333 


549 


015 


1098 


1831 


5 


100 


217 


326 


395 


652 


1087 


1304 


2174 


4 


130 


200 


300 


473 


781 


1301 


1562 


2003 


3 


154 


309 


463 


562 


927 


1544 


1854 


3080 


2 


179 


S58 


586 


650 


1078 


1788 


8146 


8878 


1 


209 


418 


626 


759 


1253 


2088 


2506 


4178 





240 


481 


721 


874 


1442 


2402 


2884 


4805 


00 


279 


558 


836 


1014 


1674 


2788 


3347 


5577 


000 


322 


644 


965 


1172 


1931 


3217 


3862 


6435 


0000 


S7S 


744 


1116 


1S6S 


SSSl 


8717 


4468 


7488 


250000 


413 


827 


1240 


1503 


2480 


4132 


4060 


8264 





mairl« Coadnctor Gable* 


, JL.C 


. or D 


. G. 












Volts. 








Siiein 


















B. & S. G. 


125 


250 


500 


1100 


2200 


3300 


6600 


11000 










Kilows 


kttS. 








6 


8.0 


16.0 


32 


70 


141 


211 


422 


704 


5 


9.5 


19.0 


38 


84 


167 


251 


502 


836 


4 


11.4 


22.8 


45 


100 


200 


300 


601 


1001 


8 


18.6 


87.0 


64 


119 


838 


886 


718 


1188 


2 


15.6 


31.2 


62 


138 


275 


413 


825 


1375 


1 


18.3 


36.5 


73 


161 


321 


482 


964 


1006 





21.0 


42.0 


84 


185 


370 


554 


1109 


1848 


00 


24.4 


48.8 


97 


215 


429 


644 


1287 


2145 


000 


S8.1 


66.S 


lis 


848 


496 


748 


1486 


8478 


0000 


32.5 


65.0 


130 


286 


572 


858 


1716 


2800 


900000 


40.4 


80.8 


162 


355 


711 


1066 


2132 


3558 


400000 


48.8 


97.5 


195 


429 


858 


1287 


2574 


4200 


500000 


56.3 


112.5 


225 


495 


990 


1485 


2970 


4M0 


600000 


68. 1 


186.S 


868 


656 


nil 


1667 


8888 


8886 


700000 


69.8 


139.5 


279 


614 


1228 


1841 


3683 


6138 


800000 


75.9 


151.8 


304 


668 


1335 


2008 


4006 


6677 


900000 


81.3 


162.5 


326 


715 


1430 


2146 


4290 


7150 


1000000 


86.9 


173.8 


348 


764 


1529 


2294 


4587 


7645 


1100000 


92.5 


186.0 


870 


814 


1628 


2448 


4884 


8140 


1200000 


97.5 


195.0 


390 


858 


1716 


2574 


5148 


8580 


1400000 


107.1 


214.3 


429 


943 


1885 


2828 


5656 


9427 


1500000 


111.9 


223.8 


448 


985 


1909 


2954 


5907 


9845 


1600000 


116.6 


tss.s 


467 


1086 


8068 


8078 


6168 


10888 


1700000 


121.3 


242.5 


485 


1067 


2134 


3201 


6402 


10670 


1800000 


126.3 


252.5 


505 


nil 


2222 


3338 


6666 


11110 


2000000 


135.6 


271.3 


543 


1104 


2387 


3581 


7161 


11935 



These tables are based on the recommended current carndng capacity dt 
cables given on pMtge 215. A power factor » 1, was used in the calcula- 
tion and hence the values found in the last table are correct for direct 
currents. For alternating currants the kilowatts given in both taUes 
must be multiplied by the power factor of the delivered load. 



FUSING EFFECTS OF ELECTMC CURRENTS. 217 



Fvsnro XFVJBCx* ojf kubcvmo cviuunriw. 

By W. H. Preeoe, F. B. S. See " Proo. Roy. Soc.," toI. xUt., March 15, 1888. 

The Law — 7 r= cufi , where /. current ; a, constant ; and d, diameter — 
ii strictly followed; and the following are the flnal yalnes of the constant 
*'a," for the different metals as determined by Mr. Preeoe : — 



Copp« . . 

Alomlnnm 

Platinum 

German Silver 

Platinoid 

Iron . . • 

Tin . . . 

Alloy (lead and tin 2 to 1) 



AliOJi 



Inches. 

10,2M 
7,585 
5,172 
6,230 
4,750 
3,148 
1,642 
1,318 
1,379 



Centimeters. 

2,530 

1,873 

1,277 

1,292 

1,173 
777.4 
406.5 
326 JS 
840.6 



Millimeters. 
80.0 
69.2 
40.4 
40.8 
37.1 
24.6 
12.8 
10.8 
10.8 



Cable CSlTiBs* 



tte ]MaHiet«m of Wires mt Variooa Mnierl* 
^ITklcM frill He I'vaed kj a Current of Olrea 

Mreafftb.— W.H.Preece,F.B.S. d=-/^^*/' 



- i^r 



^ 


Diameter tn Inches. 


3 . 


A 

^ 




II 


Silver. 
6230. 


a-* 


31 




|y 


• 


n 


§11 

5« 


|! 


u\\ 


111 






it 


III 
3© 


1 


^(Wffl 


O.0026 


O.0083 


O.O0R3 


O.O086 


0XNM7 


0.0072 


0.0083 


0.0061 


2 


OuO094 


0.0041 


0.0063 


0.0063 


0.0066 


0.00^/4 


0.0113 


0.0132 


0.0128 


S 


OU0944 


OJ0064 


0.0070 


04W69 


0.0074 


0.0097 


0.0149 


0.0173 


0.0168 


4 


ftflffiCff 


Oi»66 


O.0064 


0.0084 


0.0089 


0.0117 


0.0181 


0.0210 


0.0203 


6 


(MUffi 


CM»76 


0*0008 


OJ0097 


0.0104 


0.0136 


0.0210 


0.0243 


0.0236 


10 


OiNM 


0.0130 


0.0165 


0.0154 


0.0164 


0.0216 


0.0834 


0.0386 


0.0876 


tf 


<Mn29 


Oi»fi8 


0.0208 


0.0202 


0.0215 


0.0283 


0.0497 


0.0606 


0.0491 


» 


OjOUa 


0^191 


0.0246 


0.0245 


0.0261 


0.0843 


0.0629 


0.0613 


0.0686 


S 


OjOlgl 


0.0222 


0.0286 


0.0284 


0.0903 


0.0898 


0.0614 


0.0711 


Oj0690 


38 


fltjfflMg 


0.0250 


O.0323 


04»20 


a0342 


0.0460 


0.0694 


0.0603 


0.0779 


as 


OJ0SS7 


0.0277 


0.0368 


0.0366 


0.0379 


0.0498 


0.0769 


0.0890 


0.0864 


49 


OJQMS 


0.0903 


0.0391 


0.0388 


0.0414 


0.0645 


0.0640 


0.0973 


0.0944 


« 


Oj02B8 


0ii328 


0.0423 


0.0420 


0.0448 


0.0689 


0.0009 


0.1062 


0.1021 


» 


0j0288 


Oin62 


0.0454 


0.0460 


0.0480 


0.0632 


0.0975 


0.1129 


0.1096 


m 


0iQ326 


0^1397 


0.0613 


O.O609 


0.0642 


0.0714 


0.1101 


0.1275 


0.1237 


10 


O-Offffff 


0.0M0 


0.0668 


0.0664 


0.0601 


0.0791 


0.1220 


0.1413 


0.1371 


m 


0JB94 


0.0481 


0.0621 


0.0616 


0.0657 


0.0864 


0.1334 


0.1544 


0.1499 


» 


ojotas 


0.0620 


0.0672 


0.0667 


0.0711 


0.0936 


0.1443 


0.1671 


0.1621 


100 


QMBI 


0iffi68 


0.0720 


0.0716 


0.0762 


0.1003 


0.1648 


0.1792 


0.1739 


139 


OL0616 


0JM30 


O.0814 


0J06M 


0.0861 


0.1133 


0.1748 


0.2024 


0.1964 


149 


OJBSn 


O.O098 


0.0002 


0.0696 


0.0054 


0.12B5 


0.1937 


0.2243 


0.2176 


m 


ff^flff 


0X^763 


O.0086 


0.0978 


0.1043 


0.1372 


0.2118 


0.3462 


0.2379 


rm 


OUO078 


0.0626 


0.1066 


0.1068 


0.1128 


0.1484 


0.2291 


0.2652 


0.2673 


m 


0J1T86 


0.0686 


0.1144 


0.1135 


0.1210 


0.1682 


0.2467 


0.2846 


0.2760 


2B 


OJ079i 


OJ0868 


0.1237 


0.1228 


0.1309 


0.1722 


0.2658 


0.3077 


0.2986 


:«• 


a08U 


0.1028 


0.1837 


0.1317 


0.1404 


0.1848 


0.28bl 


0.3301 


0.3208 


^zs 


0i»B7 


0.10B6 


0.1414 


0.1404 


0.1497 


0.1969 


031R8 


0.3518 


0.3413 


m 

' - 


OljfflffO 


0.1161 


<U408 


0.1487 


0.1686 


0.2086 


0.3220 


0.3728 


0.3617 



1 



21S PBOPERTIES OF CONDUCTORS. 

By Harold Pbndbr, Ph.D. 

The aooompanying oharta* (No. 1 for loii^ spanB, No. 2 for short spaiMi} 
enable one to determine without arithmetical computation the variatiaa 
ol the tension and sag in copper wire spans with the temperature and resoK 
tant load on the wire. Similar charts can be readily prepared for wires «f 
any material. 

The symbols used in the discussion below are as follows: 

m -" wei|iit of wire per cubic inch in pounds, 
a -> coefficient of linear expansion of wire per degree Fahr. 
M ■" modulus of elasticity of wire (pounds — square indi). 
P •* ratio of resultant of the weight of wire, the weight of sleet and the 

wind pressure to the weii^t of wire. 
I — length of span in feet. 
( — rise in temperature in degrees Fahr. 
T <-• tension in thousands ol i>ound8 per sc^uare inch. 
D a- deflection at center of span in feet in direction of resultant force irtieo 

points of suspension are on the same level. 
8 •" vertical sag at center of span in feet when points erf support are oa 
the same level. 

The lines on the charts are plotted as follows: 

The hyperbolic curves on the ri^t have the equation y » f^J iriiere y 

is the ordinate and T the abscissa. A curve is plotted for p •* 1.0, 1.2, 
1.4 . . . 4.0. The value of p for each curve is indicated at the top of the 
chart. It is to be noted that the horisontal distance between these curves 
at any level is directly proi>ortional to the increment in the value of p. 
These curves are independent of the material of the wire. 

The inclined strai^^t lines have the equation y » T-jr= — ^ T. For a 

given matmal the equation of these lines depends only on the length of the 
span. The lines on the charts are drawn for copper wire for whidi m ■- 
0.321 and Af ■-> 12 X 10". The corresponding length of span is indicated 
on the right-hand margin ci the charts. For any other material, the line 
for a given length of span will have a different slope. 

The temperature scale on the X axis to the right of the origin is laid off 
so that X — Ma t. The scale given on the chart is for oopper, for whidi 
Jlf » 12 X 10« and a » 9.6 X uT*. This scale will be different for any 
other material. 

The parabolic curves on the left of the chart have the equation D -> 0.0015 

m P ^fy, where D is measured off from the left of the oripn. For a gives 
material these curves are fixed by the length of the span. The curves 
p;iven on the chart are for copper, for which m — 0.321. The oorreepond- 
ing lengths of span are indicated on the curves. These curves 'mil be 
different for any other material. 

Rules for tlie 17e« mt t1i« CMarta. 

Given: A span of length I and the points of support on the same level, 
tension Tt; ratio of resultant force to weight of wire^ pi; to find the tension 
T when the temperature rises t degrees and the ratio of resultant force to 
weight of wire changes to p (for example, sleet melts off). 

At the point 1 (Pig. 27) on the curve corresponding to pi and having 
the abscisiia 7^i, lay off 12 <» the ordinate of the point 3 on the line corre- 
sponding to { having the abscijisa t on the temperature scale. 

* These charts were devised to obtain a graphical solution of the equa- 
tions deduced by the author in an article in the Electrical World for Jan. 
12, 1907, Vol. 49, p. 99. The present article also appeared in the BlectneiU 



World for Sept. 28. 1907. 



i 



WIRE SPANS. 



219 



Throusfa 2 draw a line parallel to the line I : the abecissa of the point 4 
Miere this line outs the curve oorresponding to p ia the tension T at the 
lem^eratuFe t when the ratio of resultant force to weight of wire is p. The 
■hsciasa of the point 5 where the horixontal line through 4 outs the para- 
bolic curve co r re sp onding to { gives the corresponding deflection D at the 
cater of the span in feet. Instead oi actually drawing the straight line 
M. a pair of oompassee may be used; i.e., lay on the distance 12. then open 
the compa s e e s until the lower ooint touches the straight line I; then keep- 
ing the compaaees vertical, diae the lower point along 2 until the upper 
point intereeets the curve corresponding to p. If < is negative, i.s., if the 
temperature decreases, lay off 12 in the opposite direction. To determine 
D with greater accuracy use the formula 

D - .0015 m P ^ • 




Fig. 25. 



C«lc«latloM 9f p. 

Let w — wel^t of wire in pounds per foot. 

The weif^ttt ideet (and hemp core, if any) in pounds per foot of wire is 



w, - 0.314 W - d*) + 0.25 <V, 

where d is the diameter of the wire, di the diameter over sleet and dp the 
<fiaraeter oi the core, all in inches. 
The wind pressure in pounds per foot of wire is * 

10S - 0.00021 F2 du 

where V is the actual wind velocity in miles per hour; di — d in case of no 
rieel. The relation between indicated wind velocity (as given by U. S. 
Weather Reports) and actual velocity is as follows: 



The ratio p is then 



Indicated Velocity. 

10 
20 
30 
40 
50 
60 
70 
80 
90 
100 



Actual Velocity. 

9.6 
17.8 
25.7 
33.3 
40.8 
48.0 
55.2 
62.2 
69.2 
• 76.2 



-/O-^M^)' 



* H. W. Buck in Transactions International Electrical Congress, 1904. 



r 

220 FROPEBTIES OF CONDUCTORS. 






1 < 

ii i 



222 PROPERTIES OF CONDUCTORS. 



Oalcnlatfon of V«rMcal Aar. 

In case of no wind the vertical sag S is the same as the deflection D, 
The wind pressure gives a horizontal component to the resultant force si 
that the vertical sag when wind is blowing is, 



5- 



D 



v/^ - (i^r 



Exampls: A No. 00 stranded copper cable is to be strung in stall air 
at 70° F. between two points on the same, level 800 feet apart, ao that at a 
temperature of lero degrees Fahrenheit, with a coating of sleet i inch thi^ 
all around and wind blowing perpendicularlv to the cable at o5 miles aa 
hour factual velocity) the tension in the cable will be 30,000 lbs. per tn. 
in.; (1) at what tension must the cable be strtmg and (2) what will be the 
vertical sag at stringing temperature, i.e., 70^ also (3) what will be the sag 
at sero temi>erature when the cable is coated with i-in. of sleet and ^rina 
is blowing with a velocity of 65 miles an hour, and (4) what will be the sag 
at a temperature of 150°, in the still air ? 

We have 

w -0.406 

101 - 0.314 (filS* - 0418*) - 0.426 

tDi- 0.0021 X 66* X 1.418 - 1^. 

Therefore, at sero degrees with wind and sleet, 

. //, ^ 0.425V . /1.28 V « ^« 

(1) Measure off with compasses, on chart No. 1, the vertical dtstaaee 
from t — 70 on JT axis to the straight line corresponding to 2 = 800. Lay 
this distance off vertically above the point on the curve corresponding to 
p « 3.72 having the abscissa T — 30. Keep the upper point fixed, open the 
compasses until the lower point touches the line I -■ 800; then, keepmg tiw 
compasses vertical, slide the lower point along the line I » 800 until the upper 
I)oint intersects the curve « 1 at 7 — 8.d5: the cable must therefore be 
strung at a tension of 8950 lbs. per so. in. (2) The abscissa of the point 
on the parabolic curve I — 800, having the same ordinate as the point 
corresponding to p « 1 and T *- 8.95 is I> «- 34.4 feet, which is the vertical 
sag S, in still air at 70° F. 

(3) The deflection at sero degrees with sleet and wind is the abscissa 
of the point on the parabolic curve { — 800 having the same ordinate as 
thepoint corresponding to po — 3.72 and To — 30. i.e., Dq — 38.2 feet. 



The vertical sag is 



8 - 3^-^ - 21.afeet. 



\/^ - CiD" 



(4) to find the sag at 150° proceed as under (1) and (2) taking ( - 150. 
The sag will be found to be 5 — 36.8 feet. 



WIRE SPANS. 223 



Wire /iBspeadMl fToat Palate mot on tbe BtiWM ILmrmii, 



The charts also apply directly to the determination of the change in 
Uoiion in spans when the {Mints of support are at different heights. In 
Ihis case, howevar, the vertical sag iSi ^ — deflection in case of no wind) 
below the hij^eet point of support is given by the formula 



5.-s(i + A)' 



wher e h h the difference in height of the two points of support, and 8 is the 
mtiesl ng for a span of equal length, but points of support on the same 
^erd: 8 is calcmlaten by the formula given above, t.e.. 



5- 



V \io + tPi/ 



D befais the deflection, taken directly from the chart, for a span of equal 
iCDgth but points of support on the aame level; in case of no wind 8 •» D. 
The distance of the point of maximum sag from the highest point ot support 



2V ^ 4 8/ 



When k is greater than 4 S the lowest point of support is the point of max- 
raom sag. i^., the lowest point in the span. 

Saompie; In the example given above, suppose the difference in height 
of the points of support is 20ieet : Then (1) the tension at 70° will stiU be 
80S0 lbs. per sq. in. (2) The corresponding vertical sag at 70** in still 
■ir for points of support at same levd is 34.4 ft., therefore, for the span 
tmder consideration the vertical sag from the highest point of support ie 



(3) The vertieal sag at sero degrees with sleet and wind for points of 
npport on the same level is 21 ft.; therefore, for a 20-ft. difference in the 
Bo^t of points of support the vertical sag from the highest point of sup- 
port is 

(4) The vertical sag at a temperature of 150°, for points of support on 
the lame levd is 36.8 ft.; therefore, for a 20-ft. difference in height of the 
VmU of support the vertical sag from the highest point cdF support is 

The aeeompanjring table, giving the value of T and p for various values 
of y * Usj will be found useful in plotting the hyperbolic curves in case one 



to make charts on a larger scale than those given herein, or similar 
cherts for wires having different con.itants. The other lines are readily 
plotted from the equations given above. 



224 



■» 



1 





I 

9 
1 

> 

8 

i 



^ 



8 

1 

I 

I 

9 



& 



•8 

9 

2 



00 
CO 



CO 



CO 



00 



o 









o 



« 

09 



O 



00 



N 



9 

> 



I 



PROPEBTIES OF CONDUCTORS. 



Sr-o (D*-io iHcor- ooioo r«<0<D moo o^c« 



■ea 



OOOft^ C9>C 



^ SSS I^SS SSSS 9SS S&{3 sss ss 



8»3 SS8 



otoftiH iHr-o >o<-4b- fHe>4<« oo*-) e«o 



r-4 iHr-irH 0<nS COCOCO 9<<I<S SSS t^SS SS 



oKa» cotoo 0010(0 ^a»o e^icak a»oot«> Oioa» oco 



00 00 Oft 



;:ss S^^ S3S 39S SSlg f^SSS ss 



Sci^ t»wo 3o^ t»oo ootiH oou)^ oooo «»o 

h>aoaft oc^r^ c»^«p odih^ oocqoq mr«e4 ootot^ r«ei 
r^^r-t *HC«cl cicoeo m^9 iSioo Sh-S S< 






OMO O0eoe« <DiH^ 0«>«D C9«4 



i^b-00 oe^cD 



S2S ^^^ ^^n ^^"Qi S2S St^SS S9 






eoc>)o 



OtoQO OkvHiO 



1-i-H fHC404 



"*^^0 iOI^^ ^h-00 

St-s" eoooci h-'Q'<^ 
040405 coco^ ^SSttb 



0^'« 901 






^F>K> ooioo i-<ooto 



VDCDb* OOO^ 



»-i»-iOI 



t<*<DO eoi-4«o cooovH 

nnS w«» 5^13 



0(D-« too 



«0MO9 OQiQ 



00 CO 04 



ooaft^3 



S8? 



I0> 
iOXO) 



Ot»0 rH<DX WOftiO 

^sis ini 4^^ 



0*Hf4 C^CQ 



ciQor« c«0 

ioSS<D 00^4 



t^04O 
CO 00 CD 



u)00 

r-oo'oi 



I to 1-4 



coco 00 



CO 0)0 

S04S 



000 A 
COCOCO 



OtCDOO 



eo9'^ 



Ot^Q 9C0 



^*»o«o 



Scoo 

<O00iH 



- .2500 



04IO«0 



S»H« 



OOOM 

f-«o5oi 






00 01 01 



eoco^ 



O0400 <D'<f 

m ii 



^0610 
-^'■^'10 



OKQO 

CO too 



iO^( 



ot^o 



ICO 

i-lTflO 



SS8 

«>«o' 



"^00 CO 



<ooo»o 
cocora 



OtN.«0 C9'« 



oih>a 
ocoS 



^^^ 



sss 

loooi 



OftCOr^ 

eob-oo 



loo'oo' 



1F-I04IO 



O09C0 lOOOO QCf>«Q 
vHi-ir^ ^^^M^^ ^0«04 



lo^a 



OC4IO 






O)i0 



coco^ 



id CD 00' 



"^i-ir^ 
«coo« 



04^04 



04«-iQ 
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06b-«D 



C0O04 



Oooco coo 



OltOi-i 

coco^ 



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2§2 

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9^S 

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ssr 



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ooiOco 



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»-l04O« 



0000 

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eg 00 



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04*04 04 



OOOQ 

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O-^oo 



CON 



t« ^040 

^r-co o^^ fiSSS^ i-iihS 
eqr-iiH «hoo 000 000 



.100 



»io 00 

18 si 



WISE SPANS. 



i 



Orculai Mils 

Fm. 28. — Tbetop bounduT of eaoh mma diunm is dnwD for 

ul(10° F>hr.: the bottom Vmndsry line forO°. Far other lenL, 

mterpolftte or exterpoLatA proportionately. For mecluiDictU reuioas it 
■at raooimiiaiided to itring JAri^er ciiee of wire tlun appear in mny c]of 
^■B diuimm, ■-^"' '- ■' — **-^ — ■-- -' *!-— ^- 1 




226 



PROPERTIES OP CONDUCTORS. 



Ilellectloas Im Veet 



of fttnuided 
•tiU 



H. W. Buck. 



Wire stnmff so that the mudnmm tanston at mtnlmnm temperatDre of 
Qo F with wind blowing »t 06 milM per bow (Mtaal Telooity) will be 14,009' 
Ibe. per iqiiare in^. 



Bpenin 
Feet. 


Area 

of Wire 

inCir. 

Mils. 


1 
Degrees Fahrenheit Rise above Minimum Temperature. 


0« 


2ff> 


40'* 


60** 


80** 


lOO'* 


120* 


140*" 


150" 


200 


558.150 
266.400 
132,300 


.42 

.45 
.46 


.51 
.52 
.55 


.66 
.66 
.60 


.83 
.85 
.92 


1.07 
1.13 
1.30 


1.57 
1.65 
1.82 


2.20 
2.27 
2.45 


2.76 
2.80 
2.95 


2.97 
8.03 
3.10 


400 


563.160 
266.400 
132.300 


1.80 
1.95 
2.20 


2.20 
2.42 
2.75 


2.70 
2.90 
3.40 


3.35 
3.70 
4.20 


4.15 
4.50 
5.10 


5.05 
5.45 
6.00 


6.00 
6.40 
7.00 


6.90 
7.35 
7.85 


7.20 
7.78 
8.50 


600 


558.150 
265.400 
132,300 


4.3 

5.1 
6.2 


5,1 
6.1 
7.2 


6.0 
7.1 
8.4 


7.0 
8.2 
9.7 


8.2 

9.5 

11.0 


9.5 
10.8 
12.2 


10.8 
12.0 
13.3 


11.9 
13.1 
14.4 


12.5 
13.6 
15.7 


800 


553.150 
266.400 
132.300 


8.4 
10.3 
14.0 


9.5 

11.7 
15.4 


10.8 
13.2 
16.0 


12.3 
14.7 
18.3 


13.8 
16.4 
19.6 


15.4 
17.7 
29.0 


16.9 
19.1 
22.2 


18.3 
20.4 
23.4 


10. 
21.5 
25.5 


1000 


553.150 
265.400 
132.300 


13.9 
18.6 
26.0 


15.6 
20.3 
27.6 


17.8 
22.0 
29.0 


19.1 
23.8 
30.5 


20.8 
25.5 
31.8 


22.5 
27.1 
33.1 


24.2 
28.6 
34.4 


25.9 
30.0 
36.8 


26.7 
31.5 
37.5 



•m XmcIm 



of AtnuidoA 
•tin Air. 

H. W. Buck. 



iriro tM 



Wire stnmg go that the maximum tension at minimum temperature of 
0^ F with wlna blowing at 06 miles per hour (aotual Teloeity) ml be 14/no 
lbs. per square inch. 

Gsloulatiions made for No. 2 B. and S. stranded conductor, but it is safe 
to follow this table for all sixes of cable, for the lar^ sixes will ha.v9 
slightly smaller deflections without exceeding their elastic limit on account 
of their greater relative strength. 



Decrees 
Fahren- 




Length of Span in Feet 


r 




heit Rise 














above 














Minimum 


200 


180 


160 


140 


120 


100 


Temp. 

















6.3 


5.3 


4.2 


3.1 


2.2 


1.7 


10 


7.0 


5.7 


4.5 


3.4 


2.4 


1.8 


20 


7.8 


6.4 


5.1 


3.8 


2.8 


1.9 


30 


8.8 


7.3 


5.8 


4.6 


3.2 


2.2 


40 


10.2 


8.4 


6.7 


5.2 


3.8 


2.7 


50 


12.0 


9.8 


7.8 


6.4 


4.6 


3.3 


60 


14.0 


11.6 


9.4 


7.5 


5.6 


4.0 


70 


16.5 


14.0 


11.5 


9.2 


7.0 


5.2 


80 


19.8 


17.0 


14.3 


11.4 


8.9 


6.8 


90 


23.1 


20.0 


16.8 


13.8 


10.3 


8.8 


100 


26.6 


23.3 


20.0 


16.6 


13.1 


10.8 


110 


29.8 


26.6 


23.0 


19.5 


16.6 


13.1 


120 


33.5 


29.8 


25.8 


22.2 


18.7 


15.2 


130 


36.8 


32.8 


28.7 


24.5 


20.8 


17.2 


140 


40.0 


35.8 


31.6 


26.8 


22.8 


18.8 


150 


43.0 


38.4 


33.6 


29.1 


24.8 


20.3 



DIELECTRICS. 



227 



Valves of SmcIIIc Xsd«ctfve Ciftpaciljr •f 
Vartoo* iMelectfiok 

NaD-eonduetins materials or Izwnlaton are called dieleetriea. Tbe di- 
veetxie eoostant or speeifio indiietlve euaeity of a dieleotrie is the ratio 
of tile capacity of a eondenser havinc the apace between its plsAcs filled 
vith this substance to the cmMtdty of the same condenser with this spaoe 
filled with air. 

AD gases and vacuum 1.00 

Glass 3to8 

IVeated paper used in manufacture of power cables 2 to 4 

Poroelain 4.4 

Ebonite 2.5 

Outtanpercha 2.6 

Pure ^va Rubber 2.2 

Vulcanised Rubber 2.5 

Paraffin 2.3 

Rosin 1.8 

Pitch 1.8 

Wax l.« 

Mica 

Water 80 

Tupentine oil 2.2 

Petroleum 2 



of IHelectiica a* abo«t Mr> C. 

I are approximate value^ the resietance of dielectrics varies greatly 
vith their punty and method of preparation. 



Material. 



Ebooite 

Glsa» flint 

GtasBk ordinary 

<jtitka-percha 

lfie»7T 

{ficsnite cloth . . I ! . ! 

wcsnite paper 

Oaasbeetos 

Olhreoil 

Onkerite (crude) 

raiMr, parchment 

I^^lcr, ordinary 

Treated paper used- in manufacture of power 

cables 

Paraffin ....• 

Paraffin oil 

Bhdlse 

Vukaniaed fiber, black 

Vokanind fiber, red 

Vuleaaiied fiber, white 

Wood, ordinary 

Wood. para£Bned 

Wood, tar 

Wood, walnut 



Resistance in 


Resistance 


Millions of 


in Millions 


Megohms per 
Cubic Centi- 


of Meg. 


ohms per 
Cubic Inch. 


meter. 


14 


5.22 


28.000 


1.100 


20,000 


800 


90 


80 


450 


180 


80 


30 


2.500 


900 


300 


120 


1.200 


600 


850 


315 


1 


0.4 


460 


180 


0.03 


0.01 


0.05 


0.02 


10 to 20 


4to8 


24.000 


13.000 


8 


3 


9.000 


3,600 


68 


27 


10 


4 


14 


6 


600 


250 


3.700 


1.500 


1,700 


670 


60 


20 



{ 



228 PROPERTIES OF CONDUCTORS. 



The wistionB in reaistance of dieleotrics with temperature is muoh mon 
rapid than in the case ol mf»tal8. The variation can be exproMed by an 
exponential equation. 

fio ■• R/i • 

Where R9 ■■ resistance at standard temperature. 

A| « resistance at tempo'ature diflPerins t degrees from standard 
temperature. 
t — temperature, 
a -■ constant depending on the material. 

For gutta-percha, I in <* C a - 0.88 

For pure rubber, < in ** C a « 0.06 

For other substances, the processes of manufacture vary too widely to 
permit the establishment of temperature coefficients. 



IMelectrlc Atresir^ of Mnawlattagr HEatorlala. 

C. KiNEBRumncB. 

Let V >■ Voltage required to puncture a given tluokness of material. 

V <> Volts required to puncture a sheet of material .001 inch thiok. 
t "■ Thickness of the material in thousandths of an inch. 

For aU the materials given in table below, ezo^t pure para. 

For pure para, 

For all the materials jD^iven below, except ordinary paper and impreg- 
nated paper, tlie pimctunng voltage is the same for a solid sheet of matorial 
as for a sheet built up of thin layers. In the case of ordinary paper and 
impregnated paper the puncturing voltage is proportional to the number 

of layers ; t.a., V "■ ntfVf', where n is the number of layers and t the 
thiclmess of each layer. 

Punaurino Voltaget for Sheet .001 in, thick (v.) 

Presspahn 117 

Manila paper 56 

Ordinary paper 37 

Fiber 67 

Varnished paper 207 

Red Rope paper 239 

Impregnated paper 107 

Varnished linen 260 

Empire cloth 201 

Leatheroid 73 

Ebonite 082 

Rubber 602 

Gutta-percha 464 

Fktra 370 



I>I£L£CTRIC8. 229 



The 'vmloM in the preeedinc table are for ieeta made under the foUow- 
ins oonditioTui: 

1. ESeetiodee, flat disks with round edges 1.5 inches in diameter. 

2. Pressure on deetrodes 0.5 pounds per square inch. 

3. Voltage curve sinusoidal. 

4. Frequency of the alternating current between 20 and 76 oyoles per 

second. 
6b Temperature 17* C, humidity of the air about 70 per sent, 
d. iPniiure applied for 16 minutes. 



Pure rubber is a liquid gum having a spedfio gravity of .015. The 
mUser of eommeroe is obtained by coagulating this gmn by various means, 
the zDoet approved method being by the hot v^;x>r rising from a smudge 



madefinom oily nuts. Rubbers prepcved in this way are called "Para" 
rubbers; Ftea is the name of a province of Brasil which supplies a large 
quantity of this kind of rubber. Vulcanised rubber is a mixture of this 
lypegTiletiwI gmn, thoroughly cleaned and dried, with sulphur. Pure rubber 
deieriocBtes rapidly, whereas vulcanised rubber is oomt>arativelv stable, 
and at the same time retains the properties which make it valuable as an 
«'*«"'r*i"g material. The amount of sxilphur present varies from five 
to twenty per cent of the entire mass, the amount determining the hardness 
of the proauet. Rubber with a large admixture of sulphur is called vari- 
oolv *Miaid rubber," "vulcanite" or "ebonite." Vulcanised rubber is 
asea largely for insulating cables of all kinds. 



loaa for 30% Rvbber laavlattav Cobs; 

AdopUd 1906, by the following wire manufacturers: 

Ameriean StttA A Wire Go. Indiana Rubber A Ins. Win Co. 

Eleetrical Works. National India Rubber Co. 



Bishop Gtttta Pereha Co. New York Ins. Wire Co. 

Cenanian Qen. Electric Co. John A. Roebling's Sons Co. 

Creeeent Ins. Wire A Cable Co. Safety Ins. Wire A Cable Co. 

General Eleetrie Co. Simplex Electrical Co. 

Hasard Mig. Co. Standard Underground Cable Co. 

India Rubber A Gutta Pereha Ins. Co. 

The eompound dial! contain not less than 80% by weight of fine dry 
Fsxm n^ber which has not previously been used in rubber compounds. 
The compoeition of the remainiag 70% shall be left to the discretion of the 



> — The vulcanized rubber compound shall contain not more 
than 6% by weight of Acetone Extract. Tor this determination, the 
Aectcme extiraetion shall be carried on for five hours in a Soxhlet extractor, 
as improved by Dr. C. O. Weber. 

Me^hwBtoMl* — The rubber insulation shall be homogeneous in char- 
aetcr, shall be placed conoentrio^ly about the conductor, and shall have a 
tenatle strength of not less than 800 pounds per square inch. 

A sample of vulcanised rubber compound, not less than four inches in 
length snail be cut from the wire, with a sharp knife held tangent to the 
copper. Marks should be placed on the sample two inches apart. The 
aanqile diall be stretched until the marks are six inches apart and then 
imoMdiat^y rele a sed; one minute after such release, the marks shall not be 
over 2| inches apart. The samples shall then be stretched until the marks 
are 9 inches apart before breaking. 

For the purpose of theae tests, care must be used in outtinr to obtun a 
im»per sample, and the manufacturer shall not be responsible for results 
drained from samples imperfectly cut. 

MIgutslcal* — Each and every length of conductor shall ccnnply with 
the rsquif«meDts flpven in the following table. The tests shall be made at 
the Worka of the Manufacturer when tne conductor is covered with vulcan- 
lubbcTt and before the application of other coverings than tape or braid. 



230 



PROPERTIES OP CONDUCTORS. 



Tests shall be made after at least twelve hours' subiziersion in water and 
while still immersed. The Toltaffe specified shall be applied for five minutes. 
The insulation test shall follow the voltage test, shall be made with a battery 
of not less than 100 nor more than 500 volts, and the reading shall be tskea 
after one minute's electrification. Where tests for acceptance are made hj 
the purchaser on his own premises, such tests shjUl be made within ten dmya 
of receipt of wire of cable oy purchaser. 

KnapecttOB. — The purchaser may send to the works of the mannfaetnrer 
a representative, who snail be afforded all necessary facilities to make the 
above specified electrical and mechanical tests, and, also, to assure himseff 
that the 30% of rubber above 8|>ecified is actually put into the compouiKi, 
but he shall not be privileged to inquire what ingredients are used to make 
up the remaining 70% of the compound. 



SO% R«bb«r C*iiB|Mand Volte^^ Tea* for ft 

Fob 30 Minutes Tsbt, Takb 80% or Thbss Fioubeb. 

I. 



Sise. 


Thickness of Insulation in Inchea. 


A 


A 


A 


A 


A 


A 


1.000.000 to 550.000 . 










4.000 

6,000 

8.000 

10.000 

11.000 


0.000 


500.000 to 250.000 . 








4.000 
6.000 
8.000 
0.000 


8.000 


4/0 to 1 

Zto7 

8 to 14 


'8.666 


4,666 

5.000 


4.000 
6.000 
7,000 


10.000 
12,000 
13.000 



II. 



Sise. 



1,000,000 to 550.000 
500,000 to 250,000 

4/0 to 1 

2to7 

8 to 14 



Thickness of Insulatbn in Inches. 



A 



10.000 
12,000 
14,000 
16,000 
17.000 



A 



14,000 
16.000 
18,000 
20,000 
21,000 



A 



18.000 
20 000 
22,000 
24.000 
25.000 



A 



22.000 
24.000 
26 000 
28.000 



26.000 
28.000 
30,000 
32.000 



a 



30.000 
32.000 
34.000 
86000 



1 



DIELECTRICS. 



231 



Onk MxnUTS ELBCTBmCATION. 



1000000 CM. 
WCOOOC. M. 
800000 CH. 

700000 CM. 
600OOOC M. 
600000 CM. 

4oooooaic 

800000 CM. 

250000 CM. 
4/OStrd. 
3/OStrd. 
2/OStnl. 
1/0 Stztl. 
ISoCd 
2 Solid 
SSoUd 
48ofid 
6 Solid 
6 Solid 
8 Solid 
Solid 
10 Solid 
12 Solid 
USofid 





A 


A 


A 


A 


A 


• • • 








200 












235 












270 












305 












340 










850 


376 






■ • ■ 




390 


420 






• • ■ 




43!0 


470 






■ • • 




455 


500 






.. 4 


L40 


480 


520 






.. A 


kSO 


490 


535 






.. 4 


160 


500 


545 






.. 4 


190 


540 


590 






I 


»20 


580 


635 






»00 I 


»50 


015 


680 






>30 I 


m 


650 


715 






»60 ( 


(20 


690 


750 






^90 4 


)55 


720 


790 






120 ( 


380 


760 


840 


610 \ 


no I 


MX) 


880 


985 


650 : 


rso ) 


^ 


940 


1050 


600 \ 


r95 1 


)05 


1000 


1120 


750 \ 


570 1 


)90 


1110 


1260 


[ 


VX) 1 1 


»30 1( 


)60 


1200 


1340 



A 



210 

260 

290 

325 

365 

405 

450 

505 

540 

566 

580 

590 

650 

700 

760 

795 

830 

870 

920 

1060 

1130 

1200 

1370 

1470 



A 



235 

280 

325 

370 

420 

465 

530 

590 

680 

660 

675 

690 

760 

830 

900 

940 

990 

1040 

1100 

1240 

1310 

1380 

1540 

1640 



265 

315 

370 

420 

470 

526 

600 

680 

720 

750 

770 

790 

860 

950 

1040 

1080 

1130 

1180 

1230 

1370 

1440 

1510 

1680 

1780 



A 



300 

360 

420 

480 

540 

600 

670 

750 

810 

840 

860 

880 

950 

1060 

1160 

1210 

1260 

1300 

1350 

1490 

1560 

1620 

1790 

1890 



• 

A huchfer crade of ixMulaiing material is another gum, gutta-percha, 
vixidi 18 used in ite pure state. The use of this gum is confined almost 
eatirdy to the construction of the insulated core of submarine cables. 

SDeeafic gravitv. 0.0693 to 0.981. 

Weight per cubic foot, 60.56 to 61.32 pounds. 

Weight per cubic inch, 0.560 to 0Ui67 os. 

Softens at 115* degrees F. 

Becomes plastic at 120 degrees F. 

Melts at »2 degrees F. ... 

Oxidiaes and becomes brittle* shrinks and cracks when exposed to the air, 
eq>eeially at temperatures between 70 and 90 degrees F. 

Oxidatioa is hastened by exposure to light. 

OzidaAum may be delayed by covering the gutta-percha insulation with a 
tspe wnich has been soaked in preparedstocluiolm tar. 

Where gutt»-percha is kept continually under water there is no notice- 
sble detenoration, and the same applies where gutta-percha leads are cov* 
end with lead tulnng. 

Stretched gutta-percha, such as is used for insulating cables, will stand 
s strain of 1,000 pounds per square inch before any elongation. 

The breaking strain is about 3,600 pounds per square inch. 

The tenacity of gutta-percha is increased by stretching it. 

maalatoace er Cl«ila-P«rclla under PrMa«r«. — Tlie resistance 
of guttarpereha under pressure increases according to the following formula, 
when R » the resistance at the pressure of the atmosphere, and r the resis- 
tSQoe aft p pounds per square inui. 

r-B (1+ 0.00023 p). 



{ 



282 



PROPERTIES OF CONDUCTORS. 



Let D "■ diameter in mils of over gutta-percha inBuIation. 
d — diameter of cable core. 
W -* weight in pounds of gutta-percha per knot. 
w *>« weight in pounds of copper. 

Then for SoUd Cable 



D - -^/Sfiw-f 491 W. 



For Stranded Cablee. 



D - >/70.4w + 491 W 



f-V 



w 
1 4- 6.97 — • 



Approximate Electrcetatic Capacity of a gutta-percha cable per knot is 



0.19 



log D — log d 



microfarads. 



The ^ectroataUc capttdty of a ^tta-percha insulated cable compared with 
one of the same sise msulated with India rubber is about as 120 is to 100. 



) 



IHTidlay Cocttcieata for CorrwctlBr <k« 

aace of C^atte-Porclia at aaj- Xeaiperatare to tft** f • 

K. WlNNERTZ 1907. 



Degree F. 


Coefficient. 


Degree F. 


Coefficient. 


Degree F. 


Coefficient. 


95 


0.1415 


74 


1.089 


53 


6.015 


94 


0.1561 


73 


1.187 


52 


6.373 


93 


0.1721 


72 


1.293 


51 


6.722 


92 


0.1898 


71 


1.409 


50 


7.057 


91 


0.2105 


70 


1.535 


49 


7.377 


90 


0.2332 


69 


1.672 


48 


7.670 


89 


0.2574 


68 


1.821 


47 


7.943 


88 


0.2836 


67 


1.984 


46 


8.178 


87 


0.3125 


66 


2.161 


45 


8.383 


86 


0.3442 


65 


2.353 


44 


8.499 


85 


0.3833 


64 


2.562 


43 


8.585 


84 


0.4304 


63 


2.790 


42 


8.637 


83 


0.4801 


62 


3.035 


41 


8.678 


82 


0.5251 


61 


3.302 . 


40 


8.719 


81 


0.5848 


60 


3.588 


89 


8.767 


80 


0.6458 


59 


3.896 


38 


8.796 


79 


0.7066 


58 


4.223 


87 


8.834 


78 


0.7707 


57 


4.564 


86 


8.880 


77 


0.8406 


56 


4.919 


35 


8.932 


76 


0.9168 


55 


5.282 


34 


8.990 


75 


1.0000 


54 


5.650 


33 


0.053 



^ 



DIELECTRICS. 



233 



IMelectric Mve«stft of Air. 

The voltage required to break down the air between two terminals de- 
pends on the aha^ of the terminals, the distance between the terminals, 
and the constants of the circuit in series with Uie twminals. 

The following curres. published by Mr. 8. M. Kintner in the proceedings 
of the American Institute of Electrical Elngineers, give the voltage re- 
quired to break down air gape of various len^ha under various conditions. 









^^^ 








"*■" 






^"" 








■■^ 


^"" 










*- 


tt 




































u 




ift 






























< 




III 


^ 


-^ 


9 

Am 


























s-iS 


^ 


■^ 
























tr' 


<: 


^ 


?^ 




^ 




























^ 


^ 


^ 


IV 


X^ 


^ 


^>— 












1. 


















^ 



































7^ 




"? 


X^' 






















H" 

m 












A 


i 


r 


























s 


— ^ 








/. 


^ 


w^ 






HKBDLBPOIVTSI 
1 j^j.E.Bi> Currv 


PAHKOAPOVj 


BV4 




• 






u 


r 


w 








^ Jl Water SbwMUtla Q«p drculi 
lux Small Oondenaer 


u 




. 


7 












• V C 




BoBall OoBdamn In <tap Oreati 
bitldea ndtli ^maew 


IB 


I 


^ 




































E 






































• 


z 










































1 








I 






( 


1 


III 


chei 


B ^ 


t 






4 


I 






s 



( 



Fio. 29. 



With regard to the use of a spark gap for measuring high voltages, Mr. 
KmUier makes the following recommendations: 

For the measurement of sudden pressure variations, such as those pro- 
doeed on transmission lines by lightning, switching, grounds, short cir- 
^ut*, etc., where Uie use of an oscUlograph or similar device is not feasible, 
^.^isrk-gap method is very useful. It is, in fact, the only method bv 
vbidi any satisfactory quantitative results can be obtained under such 
^OBditions. 

"Wlun using a gap the writer prefers 'round nose' (hemispherical 
•welded terminals); (slightly concave shield/i placed back of and coaxial with 
toetmuals); the gap should be standardised over the range for which it 
M to he used just prior to taking measurements, and tmder as nearly the 



ne surroundings, connections, etc., as possible. This preference is based 
^xi. pc>nvenience of operation and greater freedom from erratic behavior 
Mthuformof gap. 

The aperk gap, although apparently a very simple device, requires an 
*>P«t operator to get results that are at all satisfactory.'* 



ii 



r 



234 








PROPERTIES < 


OP 


CONDUCTORS, 


1 










70 


















lU 


^ 






















66 
















y 


^ 


^ 






















80 
56 
80 

a at 














yj 


^ 


Y 


































y 


^ 


F 


































IV 


^ 


r 


































. 




p^ 




































P 












OUBVES OF JUMP DI8TANGBS 
8hleld«d Oapa. K'NoMte'Bhlelda Placed 
K'Back of Tenniaab 

9 1 Nonnal Qap 

O II Voltmeter B«irtane« In Oi4> Obcoit 

• III Water Beilatenco •• » 

• lY BmaU OoadeiiaBr t 


^^^ 






A 












B 

30 

fiS 
9A 






















r 














-<^ 








































16 


J 








































10 

5 




7 








































f 














































1 
































1 




1 






a 


1 




I 


\ 




1 








i 












Oap Distances in. Inches 

Fio. sa 



) 



Volte«« •f Micift im 

W. S. Andrkws. 



TnuMa Oil. 



Thiokness of 
Mica. 


Average Puno- 
turing Voltage. 


Thioknenof 
Mica. 


Average PuDo- 
turing Voltage. 


.001' 


8,800 


.006' 


6,700 


.0016' 


4,500 


.0065' 


6,030 


.oor 


4.600 


.007' 


7,290 


.0026' 


4,760 


.0075' 


7.400 


.003' 


5,300 


.008' 


7,700 


.004' 


5,570 


.0085' 


8,550 


.00475* 


5.950 


.01' 


8,900 


.005' 


6.050 







Specillc TMeraaal Coadvctlvltj of IMelcctrlcs. 

Wattb Through Inch Cubb. Teupbraturc Gbadibnt 1^ C. 





^>ecific 




Specific 


Name of Substance. 


Conduc- 


Name of Substance. 


Conduc- 




tivity. 




tivity. 


Air 


.0006 






Vulcanised Rubber . . 


.00105 


Glass 


.0053 


Beeswax 


.00093 


Wood 


.032 


Felt 


.00093 


Caoutchouc 


.0044 


Vulcanite 


.00089 


Guttapercha .... 
Sandy Xoam .... 


.0051 


Cotton Wool 


.00046 


.085 


Sawdust 


.00131 


Bricks and Cement 


.032 


Sand 


.00140 


India Rubber .... 


.0043 


Paraffin 


.00121 


Sand with Air Spaces 


.96 



DIELECTBICS. 



235 



ictovs for Hlffli TMMiea 



Tlie lofls of energy in a high tension tranBmiaaion line due to the bniah 
(fachaige from the wires depends on the electric pressure, the siie of the 
conductors and the atmospheric temperature and barometric pressure. 
For any given stae of conductor a certam critical electric pressure exists for 
▼hich there is a sudden rise in the curve of "loss between wires." Con- 
ductors should never be used in practice so small that the operating pres- 
sore is greater than this critical pressure. Mr. H. J. Ryan has deduced 
the following table, giving the minimum sise of conductor which should be 
used for prassures from 50,000 to 250,000 volts for a distance between con- 
ductoTB of 48 inches: 



Operating Pressure; 


Minimum Diameter 


90 per cent of Critical 
Kfleetive Volts. 


of Conductor in 


Inches. 


50.000 


0.058 


75,000 


0.106 


100.000 


0.192 


150.000 


0.430 


900.000 


0.710 


250.000 


0.990 



The equation showing the relation between the maximunx value of the 
preisure wave, the atmospheric tempa«ture and barometric pressure, the 
oiatance between the line conductors and the radius of the conductors 
for conductors larger than No. 4 B. and S. gauge is as follows: 



( 



where 



r 

9 



17.940 
450 + < 



X 350.000 



logto (^ <r 



+ .07) 



t 

b 



critical pressure at which the sudden increase in the 

brush discharge takes place, 
radius of conductors in inches, 
distance between conductors from center to center in 

inches, 
atmospheric temperature in degrees Fahrenheit. 
barometrio pressure in inches of mercury. 



PBOPBBTIES OP CONDUCTORS CARBTINO 
ALTERNATING CURRENTS. 

Bbyued bt Harou> Pkndbr, Ph.D. 

Beaides the ohmio nsiBtaaoe of a wire, Um following phenomena affeol 
the flow of aa alternating ourreat: 

Skin effeetf a retardation of the current due to the property of alter- 
nating currents apparently flowing along the outer surfaoe or Miell of the 
conductor, thus not making use of the fuU area. 

Inituiim eifecU, (a) teUtnducHon of the current due to its altemataona, 
induoing a counter JB.ALF. in the conductor; and (&) mutual induekinee, or 
the effect of other alternating current drcuita. 

CapacUv e^eeto, due to the fact that all lines or oonductors act aa deo- 
trioal oondenaers, which are alternately charged and diichaxged with the 
fluctuation* of the £Jd.F. 



The eifeeUve retUlanee of a dreoit to an alternating curmt dependi 
on the shape of the circuit, the specific resiatance, permeability, onoss 
section and shape of the conductor, and the frequency of the current. The 
current density over the cross section of the conductor is a miniTnnin at 
the cento*, increasing to a maximum at the periphery; in a solid conductor 
of large cross section the current is confined almost entirely to an outer 
shell or *'skin." The "Skin Effect Factor" is the number by which the re- 
sistance of the circuit to a continuous current must be multiplied to give 
the effective resistance to an alternating current. The following oorv^ 
formula and table give the "Skin Effect Factor" for a straight wire of 
circular cross section, the return wire of the circuit being assumed suffi- 
ciently remote to be without effect, whidi is practically the oeae in an 
afirial transmission line. 

Let R M Reristanoe of wire in ohms to a oontinuoiifl current. 

R' — Effective resistance of wire in ohms to an alternating current. 
/ "■ Cycles per second. 
A "- Cross section of wire in circular mUs. 
^ — Permeability of wire in O.G.S. units. 
I — Temperature in "C. 
a * Temperature coefficient per ^C. 



C «>« Percentage conductivity of wire referred to Matthieassn's 
copper standard at 0^ C. 

Then R'. faction of (|!|^). 

This function is a complex one, and can be represented best by the 
accompanying curve; however, for 



f:^>3xio». 



the approximate formula ^ - lO"* / p^^ +0.28 

is sufficiently accurate for all practicable purposes. 

286 



BSIK EVrCCT FACTOItS. 



« Vactan at SO° C for ■to«li*t VTIVM I 







Ctivalar CrM* •»€«• 


■T. 








Pndaet of Cir- 
tXA. 






Faotorfoi 


f'lSO. 


Cog^W,™ 


"S- 




.000 




























ffl 


loiooo'ooo 








fS 
























































































































ss 






























































































































































•9 













< 




• nib oorrcipoDds to B3£. Mdegnph win. 



238 CONDUCTOBS. 

The approxiinate formula 

For Iron (E.B.B. telegraph wire), reduces to 

~ - 479 X 10-«\/7I + J88 

for fA > 12.6 X !()• and « - 20« C. 
For Copper, reduces to 

^ - 96 X 10-« Vfl +0.28 

for M > 300 X lO* and I - 20*» C. 
For Aluminum^ reduces to 

^' - 76X IO-VM+0.28 

for M > 500 X 10* and < » 20*' C. 

ExampleB: To find the effective reeiatance of a round-wire .£ inch in 
diameter, permeability 500, oonduotivity 10 per cent, at 15 eydee per 
second and 0° C: 

|^. 15X500X10X.26X10> _^^^^^ 

R' 
From the ounre -^^ — 1.63 

or effective resistance R' •-> 1.63 R, 

To find the effective resistance of the same wire at 60 cycles per second: 

UCA 



l+ai 



7.5 X 10-w 



therefore, from formula ^ ^ 2.73 + 0.28 - 8.01 

or effective resistance R* » 3.01 R. 



AKIil* IlfOITCTCOlV Alfl» IlfDUCmrC lUBACTAHCK 

Of TSAHftninMioir cmucvixs foiuubi* 

BIT VAMMMJLMMa WUKKS. 

The CoeMcient of Self Indudion (L) of an elementarv circuit is defined as 
the ratio of the number of lines of induction produced by a current flowing 
in the circuit divided by the current in the circuit. When the conductor has 
a finite cross section the exact definition of the coefficient of self induction 
is the ratio of twice the energy of the magnetic field produced by the cur- 
rent flowing to the square of the current. 

The practical unit of self induction is the henry; sometimes the milli- 
henry is used, which is equal to tiAtv of a henry. 

The coefficient of self induction of a circuit depends on the sise and 
shape of the circuit, the cross section and shape of the conductor, the per- 
meabilities of the conductor and the surrotrnding medium, also, when the 
skin effect is large, upon the frequency of the current and the specific re- 
sistance of the conductor. The instantaneous E.H.F. induced in a cir- 
cuit by any change of the current flowing in the drouit is e ■» — -j; {Li), or, 

at 

if L is constant, which is strictly true when there is no iron in the circuit, 

and approximately so in any case, « -" ^ ^ j^ * 

When a constant RM.F. is impressed on a cirouit or coil coDtainiii|S 
iDdtfoJiMloe, the current does not reach its full value instantly, as it » 



8SLF INDUCTIOK AJfD DTDUCTITS BEACTAKCS. 239 



oppand at first by a oountar-eleetroiDotive force due to the induotanee. 
TiaB eoonter-eleetroiiiotive force gradually grows less until the current 
tttchfls its full strength, which theoretically takes an infinite time, and in 
^etiee it is usual to determine the time taken for the current to attain 
63^ of its full value and this period is called the time<on$ianU 

'nine«>nstant in seconds -■ -;: ^rT 

ohms resistance 

henrys X final amperes 

applied volts 

If the impr e s s ed E.M.F. varies according to the sine law and L is con- 
Btant, the aective value of the counter inductive E.M.F. is 

viwre / — cydes per second or frequency and / — the effective value of 
the nvTcat. 2 wfL is called the inductive reactance or simply the inductance 
of the eiremt. 

Ihe induced ELM.F. lags 90° behind the current. The E.M.F. required 
to onreome the induced £LM.F. leads the current by 00°. 



rmwmmim for BwiifMmAwugtimm a«d M«d«ctlve 

I^ r — radius of wire in inches. 



n -■ number of wire on B. and S. gauge.* 
D ■■ distance between wires in inches. ^^ 

I ■■ distance of tranomission O^^g^^ o' one wire) in 1000 feet. 
L - eoefllcient of self induction of 1000 feet of wire in millihenrys. 
~ frequency of current in cycles per second. .... 

- 2 «/L X 10^ — inductive reactance of 1000 feet of wire m ohms. 



i 



Bnreu-vBASB Cncnir — 2 Wibi 



iQ_-^-— 9 ( 



Fu. 2« 

Total self induction of circuit — 2 2L. 
Total inductive reactance of circuit * 2 IX, 



THln-PBASB ClBCITXT 8 WfRBB. 




Fi«. 3* 

Total aelf induoUon per phase (circuit formed by any two wires) ^y/ZW. 
Total inductive reactance per phase — V^S IX, 

L - 0J01524 + 0.14 logio (^ 

-0.00705n+A. 
where i4 - 0.14 logic + 0.1258. 

* Bee table on next page for values of n for wires larger than Ko. 0. 



^ 



r 



240 



CONDUGTOBS. 



Jfor UiOir 



L - 0.01624 y. + 0.14 log^o (^ 



where ^ — permeability of the iron, m varies with the qoality of the inm 
and also with the strength of the onrrent. The above formiila is ' 



only in case ^ is constant over the cross section of the wire, which in any 

Eractical case is only approximately true. The tables on p. 248 are calen- 
ited for |A — 160, corresponding to good quality telegraph wire, and. 
therefore, 

X -2.386 +0.14 logto-' 



F 


D. 


ii. 


^ 


1 in. 


.0662 
.0687 
.1083 
.1268 




■k 


2 


.1679 




n 


3 


.1925 




li 





.2347 




w 


12 


.2768 




V 


18 


.3016 






24 


.3190 






36 


.3436 






48 


.3611 






60 


.3747 




\ 


72 


.3867 




} 


V»liiea of n for IVlrca Iia 


^iV^r tluuft IVo. O, II. ai 


sd A. 




Sise. 


n. 

« 




00 B. and S. 


-1 






000 


-2 






0000 


-3 






260,000 C. M. 


-3.743 






800.000 


-4.636 






860.000 


-6.203 






400,000 


-6.783 






460.000 


-6.206 






600,000 


-6.762 






660.000 


-7.166 






600,000 


-7.644 






060,000 


-7.891 






700,000 


-8.212 




• 


760.000 


-8.612 






800,000 


-8.792 






860,000 


-9.066 






900.000 


-9.302 






060,000 


-9.637 






1.000.000 


-9.760 




L ^ 


k. 







8BLF INDUCTION. 



241 



^ 



•M Hk MilltfcwiTy pmr 1 



Nora. — The self izuiuetion of ft stranded wire is alichtly less than that 
of a aolid wire of the same cross section, and slightly greater than 
that of a soiid wire having the same diameter, but more nearly equal to 
tbat of a solid wire with equal cross section. . The exact value of the self 
induetaon of a steand is a complex expression involving both the sise and 
number of the individual wires. (See UEetairaqe Blectrique, Vol. Ill, p. 
20.) For aD practical purposes the self induction of a strand may be 
taon oqoftl to that of a solid oonductw having the flaose oroee eeetion. 

L-m .00705 n + ii. 



B.aad8. 



0000 

000 

00 



1 
a 

4 

6 

6 

8 

10 

U 

14 



Interaxial Distances. 



r 


V 




!6977 




.1117 


.1013 


.1180 


.1084 


.1269 


.1225 


.1401 


.1367 


.1541 


.1507 


.1682 


.1647 


.1822 



.0871 
.0043 
.1012 
.1083 
.1154 
.1223 
.1364 
.1436 
.1506 
.1647 
.1788 
.1928 
.2068 



1' 



.1046 
.1116 
.1187 
.1258 
.1329 
.1398 
.1539 
.1610 
.1681 
.1822 
.1963 
.2103 
.2243 



2* 


8' 


.1467 


.1714 


.1538 


.1778 


.1608 


.1855 


.1670 


.1926 


.1750 


.1946 


.1830 


.2066 


.1961 


.2207 


.2032 


.2278 


.2102 


.2349 


.2243 


.2490 


.2384 


.2631 


.2525 


.2772 


.2665 


.2911 









Interaxial Distances. 






Or. Mils and 


















B.and& 


















Gn«e. 


6» 


12* 


18* 


24' 


36' 


48' 


60' 


72* 


UOOXXX) 


.1659 


.2080 


.2327 


.2502 


.2748 


.2923 


.3059 


.3169 


900.000 


.1691 


.2112 


.2359 


.2534 


.2780 


.2055 


.3091 


.3201 


800000 


.1727 


.2148 


.2395 


.2570 


.2816 


.2991 


.3127 


.3237 


700000 


.1768 


.2189 


.2436 


.2611 


.2857 


.3032 


.3168 


.3278 


000.000 


.1815 


.2236 


.2483 


.2658 


.2904 


.3079 


.3215 


.3325 


500000 


.1871 


.2292 


.2539 


.2714 


.2060 


.3135 


.3271 


.3381 


iBOJOCO 


.1903 


.2324 


.2571 


.2746 


.2092 


.3167 


.3303 


.3413 


J0O.OOO 


.1939 


.2360 


.2807 


.2782 


.3028 


.3203 


.3339 


.3449 


850,000 


.1980 


.2401 


.2648 


2823 


.3069 


.3244 


.3380 


.3490 


800.000 


.2027 


.2448 


.2095 


.2870 


.3116 


.3291 


.3427 


.3537 


250.000 


.2083 


.2504 


.2751 


.2928 


.3172 


.8347 


.3483 


.3593 


0000 


.2135 


.2666 


.2803 


.2978 


.3224 


.3399 


.3535 


.3645 


000 


.2206 


.2627 


.2874 


.3049 


.3295 


.3470 


.3606 


.3716 


00 


.2276 


.2648 


.2945 


.3120 


.3366 


.3541 


.3677 


.3787 





.2347 


.2768 


.3015 


.3190 


.3436 


.3611 


.3747 


.3857 


1 


.2418 


.2839 


.3086 


.3261 


.3507 


.3682 


.3818 


.3928 


2 


•248« 


.2009 


.3156 


.3331 


.3577 


.3762 


.3888 


.3998 


4 


.26291 


.3050 


.8297 


.3472 


.3718 


.3893 


.4029 


.4139 


6 


.2770 


.8191 


.3438 


.3613 


.3859 


.4034 


.4170 


.4280 


8 


.2011 


.3832 


.8579 


.3754 


.4000 


.4175 


.4311 


.4421 


10 


.305^ 


.8478 


.3720 


.3895 


.4141 


.4316 


.4452 


.4562 



( 



r 



242 



C0NDUCTOE8. 



ReactMuse Im OIimm P»r lOOO feet •T fl^lM ]V«m- 
Mapnetlc IFire. 

100 Ctcles pbb Sbcomd. X >« 0.6283 L, 

NoTB. — Inductive reactance at other frequencies proportional to ▼aluet 

given in this table. 



B. and 8. 
Gauge. 


Interaxial Distances. 


r 


r 


r 


1' 


2* 


3- 


0000 

000 

00 



1 

2 

4 

5 

6 

8 

10 

12 

14 




.0636 
.0681 
.0770 
.0858 
.0946 
.1034 


ioeis 

.0702 
.0747 
.0791 
.0879 
.0968 
.1056 
.1144 


.0547 
.0592 
.0635 
.0680 
.0725 
.0768 
.0857 
.0902 
.0946 
.1034 
.1123 
.1211 
.1299 


.0657 
.0701 
.0745 
.0790 
.0834 
.0878 
.0966 
.1011 
.1056 
.1144 
.1233 
.1321 
.1409 


.0922 
.0966 
.1010 
.1055 
.1099 
.1143 
.1231 
.1276 
.1320 
.1409 
.1497 
.1586 
.1674 


.1076 
.1116 
.1165 
.1209 
.1254 
.1298 
.1386 
.1431 
.1475 
.1564 
.1652 
.1741 
.1828 



I 



Cir. Mils and 


Interaxial Distances. 


B. and 8. 


















Gauge. 


6' 


12* 


18' 


24* 


36' 


48* 


60* 


72* 


1.000,000 


.1042 


.1307 


.1462 


.1572 


.1727 


.1837 


.1922 


.1901 


900.000 


.1062 


.1327 


.1481 


.1592 


.1747 


.1857 


.1942 


.2011 


800 000 


.1085 


.1350 


.1505 


.1615 


.1769 


.1879 


.1965 


.2034 


700,000 


.1111 


.1376 


.1531 


.1640 


.1795 


.1905 


.1990 


.2060 


600,000 


.1140 


.1405 


.1560 


.1670 


.1825 


.1954 


.2020 


.2089 


500,000 


.1176 


.1440 


.1595 


.1706 


.1860 


.1970 


.2065 


.2124 


450.000 


.1196 


.1460 


.1615 


.1725 


.1880 


.1990 


.2076 


.2144 


400,000 


.1218 


.1483 


.1638 


.1748 


.1902 


.2012 


.2098 


.2167 


350.000 


.1244 


.1509 


.1664 


.1774 


.1928 


.2038 


.2124 


.2193 


300,000 


.1274 


.1538 


.1693 


.1803 


.1958 


.2068 


.2168 


.2222 


250,000 


.1309 


.1573 


.1728 


.1838 


.1993 


.2103 


.2188 


.2257 


0000 


.1341 


.1606 


.1761 


.1871 


.2026 


.2136 


.2221 


.2290 


000 


.1386 


.1651 


.1806 


.1916 


.2070 


.2180 


.2266 


.2335 


00 


.1430 


.1695 


.1850 


.1960 


.2115 


.2226 


.2310 


.2379 





.1475 


.1739 


.1894 


.2004 


.2159 


.2269 


.2364 


.2423 


1 


.1519 


.1784 


.1939 


.2049 


.2203 


.2313 


.2399 


.2468 


2 


.1563 


.1828 


.1983 


.2093 


.2247 


.2357 


.2443 


.2512 


4 


.1652 


.1916 


.2072 


.2181 


.2336 


.2446 


.2531 


.2601 


6 


.1740 


.2005 


.2160 


.2270 


.2425 


.2535 


.2620 


.2689 


8 


.1829 


.2093 


.2249 


.2359 


.2513 


.2623 


.2709 


.2778 


10 


.1918 


.2182 


.2337 


.2447 .2602 


.2712 


.2797 


.2866 



^ 



INDUCTITE BEACTAKCS. 



243 



InOlmui 99W%OOmWm$ •fS^lMiroi 



25CTGiiS8 Per SBCOZfD. X - .1571 L. 











IntaraxiA] Distaaces. 






B-andS. 












Gaoge. 
















V 


y 


f 


1* 


TT 


3' 


0000 






.0137 
.0148 


.0160 
.0175 


.0230 
.0242 


.0209 


000 






.0279 


00 








.0159 


.0186 


.0253 


.0291 











.0170 
.0181 


.0108 
.0209 


.0264 
.0276 


.0302 


1 


■ ■ • a 




.0313 


2 




.0153 


.0192 


.0220 


.0286 


.0325 


4 




.0176 


.0214 


.0242 


.0308 


.0347 


5 


•oiio 


0187 


.0225 


.0253 


.0319 


.0358 


6 


.0170 


0108 


.0236 


.0264 


.0830 


.0360 


8 


.0192 


0220 


.0259 


.0286 


.0852 


.0391 


10 


.0215 


0242 


.0281 


.0306 


.0374 


.0413 


12 


.0237 


0264 


.0308 


.0330 


.0396 


.0435 


14 


.0250 


0286 


.0325 


.0352 


.0418 


.0457 



(Tir. Mibaiid 

B.aad8. 

Gauge. 



Interaxial Distanoefi. 



1,000,000 
MXMXX) 
800000 

TOOiOOO 

eoaooo 
soaooo 

4B0M0 
400.000 

mooo 
aootooo 

250000 

0000 

000 

00 



1 

2 
4 
6 
8 
10 



6' 


12* 


18' 


24' 


36' 


48' 


60* 


72* 


.0261 


.0327 


.0366 


.0393 


.0432 


.0460 


.0481 


.0498 


.0286 


.0332 


.0371 


.0398 


.0437 


.0465 


.0486 


.0603 


.0272 


.0338 


.0377 


.0404 


.0443 


.0471 


.0492 


.0609 


.0278 


.0344 


.0383 


.0410 


.0449 


.0477 


.0498 


.0616 


.0285 


.0351 


.0390 


.0417 


.0456 


.0484 


.0505 


.0622 


.0294 


.0360 


.0399 


.0426 


.0465 


.0493 


.0514 


.0631 


.0209 


.0365 


.0404 


.0431 


.0470 


.0498 


.0619 


.0536 


.0306 


.0371 


.0410 


.0437 


.0476 


.0603 


.0626 


.0542 


.0811 


.0377 


.0416 


.0444 


.0482 


.0510 


.0631 


.0548 


.0319 


.0385 


.0423 


0451 


.0490 


.0517 


,0538 


.0656 


.0327 


.0393 


.0432 


.0460 


.0498 


.0526 


.0647 


.0564 


.03S5 


.0402 


.0440 


.0468 


.0506 


.0534 


.0656 


.0673 


.0347 


.0413 


.0452 


.0479 


.0518 


.0646 


.0667 


.0684 


.0358 


.0424 


.0463 


.0490 


.0529 


.0566 


.0578 


.0596 


.0369 


.0435 


.0474 


.0501 


.0540 


.0667 


.0589 


.0606 


.0380 


.0446 


.0485 


.0512 


.0551 


.0678 


.0600 


.0617 


.0391 


.0457 


.0496 


.0523 


.0562 


.0689 


.0611 


.0628 


.0413 


.0479 


.0518 


.0545 


.0584 


.0612 


.0633 


.0650 


.0435 


.0501 


.0540 


.0568 


.0606 


.0634 


.0655 


.0672 


.0457 


.0523 


.0562 


.0500 


.0628 


.0656 


.0677 


.0696 


.0480 


.0540 


.0684 


.0612 


.0661 


.0678 


.0699 


.0717 



( 



COITDTJ0TOB8. 



M CrcLn Pbr Sboohd. X — 0.3770 L. 



loMnxia] DiMuioaB. 



Or, WlaMid 



350.000 
300,000 



InMnxUI DiaUoMa. 



a- 


w 


w 


48* 


60* 


72* 


























































































































































































































































.67 





^ 



INDUCTIVB BEACTANOB. 



245 



of Xoop Vonsetf bj Two 
hoao XvuMMiliMion m<lii«>. 



of 



Ormb pkr 1000 Fbbt or Lnni* (Cokdvctor Non-Maonbtio ) 

100 Ctclks per Skcond. 



■^loop — ' -^for angle wire. 



Nor. — Inductiire reaotanoe at other frequenoies proportional to ralaes 
$wa in thiB table. 



1 












il.ani1.S 
Ga««e 












1' 


V 


r 


1' 


2' 


3' 


0000 






.0047 


.1138 


.1596 


.1864 


000 






.1025 


.1214 


.1673 


.1933 


00 






.1100 


.1291 


.1749 


.2018 









.1178 


.1368 


.1827 


.2094 


1 






.1255 


.1445 


.1903 


.2171 


2 




.1062 


.1331 


.1521 


.1980 


.2248 


4 




.1215 


.1484 


.1674 


.2133 


.2401 


5 


.1102 


.1293 


.1563 


.1758 


.2210 


.2478 


« 


.1179 


.1369 


.1638 


.1828 


.2286 


.2554 


8 


.1333 


.1523 


.1791 


.1982 


.2440 


.2708 


10 


.1487 


.1677 


.1945 


.2135 


.2503 


.2862 


12 


.1630 


.1830 


.2097 


.2288 


.2746 


.3014 


U 


.1791 


.1982 


.2250 


.2440 


.2898 


.3167 



Or.lCibaad 


InteraxiBl Distances. 


B.iDd8. 


















Gm«b. 


6' 


12" 


18» 


24' 


36' 


48* 


60* 


72* 


IJOOO.000 


.1807 


.2285 


.2538 


.2724 


.2992 


.3183 


.3330 


.8450 


900,000 


.1842 


.2300 


.2568 


.2759 


.3027 


.3218 


.3365 


• o4oO 


9QO.O0O 


.1881 


.2339 


.2807 


.2798 


.3066 


.3267 


.3404 


.3524 


700.000 


.1928 


.2384 


.2652 


.2843 


.3111 


.3302 


.3449 


.3569 


600.000 


.1977 


.2435 


.2703 


.2894 


.3162 


.3353 


.3500 


.3620 


6004X)0 


.2038 


.2496 


.2764 


.2955 


.3223 


.3414 


.3561 


.3681 


4604)00 


.2073 


.2530 


.2799 


.2989 


.3258 


.3449 


.3596 


.3716 


jOWOO 


.2111 


.2570 


.2889 


.3029 


.3296 


.3437 


.3636 


.3755 


S60.000 


.2156 


.2615 


.2884 


.3074 


.3341 


.3532 


.3681 


.3800 


3004)00 


.2208 


.2865 


.2984 


.3125 


.3393 


.3584 


.3731 


.3851 


250000 


.2268 


.2726 


.2995 


.3185 


.3454 


.3644 


.8702 


.3911 


oooo 


.2324 


.2783 


.3052 


.3242 


.3511 


.3702 


.8849 


.3069 


000 


.2402 


.2861 


.8180 


.3320 


.3587 


.3778 


.3927 


.4047 


00 


.2478 


.2937 


.3206 


.3397 


.3665 


.3856 


.4003 


.4123 





.2556 


.3014 


.8282 


.3473 


.3742 


.3932 


.4079 


.4199 


1 


.2632 


.3092 


.3360 


.3551 


.3818 


.4008 


.4157 


.4277 


2 


.2709 


.8168 


.3437 


.8627 


.3894 


.4085 


.4234 


.4353 


4 


.2863 


.3820 


.8591 


.3780 


.4048 


.42LD 


.4386 


.4508 


6 


.3015 


.8475 


.3743 


.3934 


.4203 


.4303 


.4540 


.4660 


8 


.8170 


.8627 


.8898 


.4088 


.4355 


.4546 


.4695 


.4814 


10 


.3324 


.8781 


.4060 


.4241 


.4509 


.4700 


.4847 


.4967 



{ 



^ Uncth o( line equals one half the total length of wire in the loop. 



CONDOCTOBS. 




;rioap - v/3 X for eioelt 



» 







Im™=^ Db.«z.«. 




















Gauge. 


i- 


i' 


I* 


1' 


2' 


3' 








0237 


028S 


039D 


























































































*02B5 


ra« 




















































14 






0563 









Cir. Mi 


,r. 




GBuge. 




I.- 


24' 


»- 


48* 


60" 


72- 


1.000 

1 
' i 


1 
1 

WO 

1 

2 
10 


;E 

:0721 

:o7a; 

fl 




Q70C 

11 

07fi7 

E 
si 

ORSR 

1 




Q7S7 

E 

nsa; 

1 

093; 

loi; 




S 

085; 
0871 
0S8.' 

OSll 

1 

i 




ii 

08W 
0909 

if 

oat 

1 




OM3 

0039 

DOSS 

0978 
0093 

IIW 

lias 



li hall the total Imgth of wire in the knp. 



INDUCTIVB 






FmBT or Iohc* (Cohdoctob Nox-ll^aHi 



Zknp — Va Jl (or HDcls wire. 













InUnzuJ Kstuion. 






B.ud& 










Gn*.. 


1* 


r 


*- 


i- 


2- 


3* 


(UOO 






0508 


0«S3 


OOSB 


1118 


on 












06UJ 




0728 


1004 


1190 


oo 












OSOO 




0774 


1049 


121L 












M3f 


i 




E 


ii 


1303 










vn« 


0B38 


















0821 


0983 






1372 


1533 










0»i4 


075 






1164 


1625 


1 




08B2 




















0083 




loss 


268 




1373 


1M8 




14 


107S 


1180 1 


3fi0 


14M 1 


1739 


1900 


CSr. Kilt and 










B.uda. 










(i»W>. 


- 








UPOO0W 


















































































































000 










00 




















10 











i 



* Uofth nf line equals one half the Ui 



J leOBth ot wire in the loop. 



248 



COKBUCTOBS. 



•elf HnducMmi 



IM ]HUlllb«av7« ptBT 1«90 Feet •f 



I, -2.286 +.14 logic (f)- 













1 






Roeblioc 


Dia. 
In. 


• 


Gauge. 






t 










.225 


1' 


2* 


3* 


6' 


9' 


12* 


18' 


24' 


4 


2.4189 


2.4610 


2.4857 


2.5278 


2.6526 


2.6699 


2.5946 


2.6121 


6 


.192 


2.4285 


2.4706 


2.4953 


2.5374 


2.5621 


2.5796 


2.6042,2.6217 


8 


.162 


2.4389 


2.4809 


2.5056 


2.6478 


2.5724 


2.5899 


2.6146 


2.6321 


9 


.178 


2.4443 


2.4865 


2.5111 


2.5533 


2.5779 


2.5964 


2.6201 


2.6376 


10 


.135 


2.4499 


2.4921 


2.5167 


2.5589 


2.6835 


2.6010 


2.6257 


2.6432 


11 


.120 


2.4571 


2.4992 


2.5239 


2.5660 


2.6907 


2.6082 


2.6328 


2.6503 


12 


.105 


2.4652 


2.5074 


2.5319 


2.6742 


2.6988 


2.6163 


2.6409 


2.6584 


14 


.080 


2.4817 


2.5239 


2.5485 


2.5907 


2.6163 


2.6328 2.6576 


2.6748 



JbudnctiTe lieactence to Olinu per 100# F«e4 of ftolid 

Iron lirire. 

100 Ctcleb Per Second. X — 0.6283 L. 

Note. — Inductive reactance at other frequencies prop(Mttonal to 
values given in this table. 



Roebling 


Dia. 
In. 

.225 
.192 
.162 
.148 
.135 
.120 
.105 
.080 






Interaxial Distances. 






Gauge. 


1' 


2* 


3* 


6' 


9* 


12* 


18' 


24* 


4 

6 

8 

9 

10 

11 

12 

14 


1.5191 
1.6251 
1.5316 
1.5350 
1 .6386 
1.5431 
1.5482 
1.5585 


1.5455 
1.5516 
1.5581 
1.5615 
1.5650 
1.5695 
1.6746 
1.6850 


1.6610 
1 .5671 
1.5735 
1.5769 
1.5806 
1.5850 
1.5901 
1.6005 


1.5875 
1.6936 
1.6000 
1.6035 
1.6069 
1.6116 
1.6166 
1.6269 


1.6029 
1.6090 
1.6165 
1.6189 
1.6226 
1.6269 
1.6320 
1.6424 


1.6139 
1.6199 
1.6266 
1.6299 
1.6335 
1.6379 
1.6430 
1.6684 


1.6294 
1.6356 
1.6419 
1.6464 
1.6489 
1.6634 
1.6585 
1.6689 


1.6404 
1.6466 
1.6529 
1.6664 
1.6590 
1.6644 
1.6605 
1.6700 



CAiPAcn nPY. c Ar Acnnr »» actawcjbl j^to ch[a»€»- 
rara cumtsif t of ntAivsmssxoM cmcuixs 

9'OlUIIEIi mr PARAIiIiBIi ^imsA. 

Whenever a difference of potential is established between two or more 
conductors a static charge manifests itself on each conductor. If there 
are but two conductors present these static charges are equal and oppMite. 
Two conductors thus carrying equal and opposite charges are said to foiiBi 
a condenser. The ratio of the otiarge {q) on one of the conductors to the 
difference of potential (e) between the two conductors is called the capa* 
city (C) of the condenser, %,e„ 



If Q is expressed in coulombs and e in volts, the unit of capacity as de- 
fined oy this eqiiation is called the farad. A capacity as large as a farad 



^ 



TBAN8MI8SI0N CIRCUITS. 249 



li ft ntftthamatieal fietion ; the mit wi^lojred in praotioe is the microfarad, 
'which u one millionth of a farad. 

Tike capacity of a condenser depends on the sise and shape of the con- 
doctora, the specific inductive capadty of the surrounding medium, and 
its distanoe from other conductors. 

Tba iofltantaneouB capacity E.M.F. is in practical units. 






and ths effective value of this E.M.F. for a sine wave current is 

10« 



S^ 



2irfC 



10* 
The cqveaaion .^ is called the capacUy reactance, or simply the cap€U!v- 

iBaee, of the circuit. The reciprocal of this quantity, namely, -r^. ib 

csOed the capacity 9U»ceptancef this is the quantity used in the treat- 
. smt of the capacity of transmission circuits. 

The earrent required to charge and discharge a condenser is called 
ths d anfing eurrerUi for a sine wave of imprened E.M.F. the chatging 
cmtntii 

7,-2 *fCB X 10-«. 

TIm oapadty E.M.F. leads the current by 90^; the E.M.F. required to 
ovveoDM the eapactiy E.M.F. lags 90** behind the current. 

Naglv-PlMiM Tirmaemisetom Mila«. — The capcuuty effect in a sin^le- 
; Plksie transmisrion line is the same as would be produced by shuntmg 
; aenai the line at each point an infinitesimal condenser having a capacity 
:*Visl to that of an infinitesimal length of circuit. The 
I {net ealculation of this effect involves the use of hyperbolic t I 

I nnetions and oonmleac algebraic quantities. A close approz- _ _ 

I matMB is to oonsioer a condenser of half the capacity of the >-''~| |~^ 
I iM ihimtsd across the line at each end. A still closer ap- I 

P^ramatton is to divide the fine into three equal parts and ' 

2J«i«r the capacity of each section concentrated m a con- Fio. 4. 
I ^"■■^ •.* the center of that section, but in most practical 
f M> this refinement is not necessary. For the purpose of calculating the 
I r^'IVJiK current tL very simple and in general sufficiently accurate method 
I i'S.^fS^P* the current taken by a condenser having a capacity equal 
wwat of the entire line when ehaiged to the pressure on the line at the 
g«Mwg end. For the calculation of the effect of capacity on the effi- 
^S~ wgahition of transmission lines see page 264. 
araree-PliaAe TnMntiaeiMt Xitee. — The capadty effect in a three- 
phase transmisrion line is the same as would 
he produced bv shuntini? the line at each point by 
tiiree infinitesimal condensers connected in star 
^th the neutral point grounded, the capacity 
of each condenser being equal to twice that of 
a condenser of infinitesimal length formed by any 
j^ two of the wires. The effect of capacity on the 

JSr^/jt p«uIation and efficiency of the line can be deter- 

^'^^ '^V^ mined with sufficient accuracy in most cases by 
Of ^Si^rj eoDsidenng the Kne shunted at eaeh end by three 

«_^ _ oondensers connected in star, the capacity of each 

"O. D. condenser being equal to that formed by any two 

A. -.«.—_« A . T''** *" *•** '™«- OSee page 264.) 
■M*wro™»te value for the charging current per wire is the current 
jgwwi to charge a condenser, equal in capacity to that of any two of the 

mSTllS Jr* P«""»® •.* ^^^ generating end of the line between any one 
*"• and the neotral pmnt. 



{ 



250 



CONDUCTORS. 



Formuls: 



Let 



r « radius of wire in inches, 
n » number of wire on B. and S. gauge.^ 
H ■" height of wires above ground. 
D ■• distance between wires in inches. 

I >■ distance of transmission Oength of one wire) ia 1000 f 
V ■■ impressed voltage between adjacent wires at generating 
Fo"" impressed volts between any wire and ground or n< 

at generating end. 
Co"* capacity per 1000 feet of a single wire parallel to the 

in microfarads. 
C — capacity per 1000 feet of circuit (2000 feet of wire) f< 

by two paralld wires. 
/ — frequency of impressed E.M.F. in cycles per second. 
2 wiC 
(iD -" ~TqF "" capacity susoeptance per 1000 feet of a single 

parallel to the earth. 

h "" -775- "■ capacity susceptanoe per 1000 feet of circuit (2 

feet of wire) formed by two parallel wires. 
K * dielectric constant of surrounding medium. For bare 
insulated overhead wires, without metallic sheath, K ■■ 

Sinrle Overficiad Wire with Bartk lt««iai 




I 



Co- 



.007354 



logio 



2H 



Total capadty of circuit ^ IC, 

Total capacity susceptance of circuit ■■ { 6. 

mi^/A^M.yMm^'jA,My//M ^otal charging current - X hV^ 



Fig. 6. 

Vwo Overhead ITi 



, SlB^le-Pliiiae. 



C - 



.003677 



k-2^--H 




1 



B + 13.7n 





Total capacity of circuit — Z C Fia. 7. 

Total capacity susceptance of drcuit— { b. 
Total charging current •» 2 b F. 

Two irirea In Oronnded MeUilllc Alieatli, AiBrl«-P^ 



.003677 K 




FiQ. 8. 



, \2a R ^ - an 

^"^'^ L'V «H^J 

Total capacity of circuit — Z C, 
Total capacity susceptance of circuit 
Total cliarging current ^ lb V. 



- lb. 



• For values of n for wires larger than No. see page 240. ^ 

t B - 272 logiQ D - 215. For values of B see p. 251. For stranded wira 
neither formula is strictly accurate: the logarithmic formula gives reaulti 
practically correct; values calculated by the second formula are about 3 pe 
cent too small. 



TBAN8MISSION CIRCUITS. 



251 



CmMeatrtc Cable la «r«aad««l Metallic Slieatb, 



JU*. C* «» oapaeity in microfarada per 1000 feet of oondeoMr fonned by 
the two eonductors. 

<y»- capacity in microfarads per 
1000 feet of oondeosa' formed by 
outer ooinduetor and sheath. 

Then C ' - ^5QI3S1^« 
^„ _ .00735Jjgt 

Total chaiKins crirrent =- / 6' F + / 6" Fo. 

Three Overliead irire», Tliree-Pliaae. 

.003677 




Fig. 0. 




q::?^ 



c- 



logio 



D 

r 
1 



O 



Fio. 10. 



B + 13.7 n 

Total capacity per wire — 2 Z C. 
Total capacitance per wire — 22b. 

Total cbaiiging current per wire *= — -=- — 2 Z 6Fo. 

V3 

la Metallic Slieatb, Tliree-Pliaae. 

.007364 if 



[3 a» (ft«j-a»)n 




To«al capacity per wire — 2 Z C. 
Total capacitaiuse per wire «> 2 Z b. 



t ^_^ 

• B - 272 lo^jo r> - 216. For vahiee see table. For stranded wirce 
n«j«r formula is strictly accurate; the logarithmic formula gives results 
J««i«ally correct; values calculated by the second formula are about 3 
<Kos too small. 



per 



PROPBBTIBS OP CONDUCTORS CARRYING 
ALTERNATING CURRENTS. 

Rbtubd bt Harold Pbndsb, PhJ). 

BendM the ohmio resiatonoe of a wixe, the foUowing phenomena a£Feet 
the flow of an altematinf current: 

Shin effeotf a retardation of the current due to the property of altera 
nating currents apparently flowizu alone the outer Burface or ahell of the 
conductor, thue not making use ofthe fuU area. 

Inductive effeeU, (a) teUinduction of the current due to its altonationfl, 
inducing a counter £.M.F. in the conductor; and (6) mntual induckinet^ or 
the effect of other alternating current drcuite. 

Capacity effeetB, due to the fact that all lines or conductors act as elee- 
trical condensers, which are alternately charged and dischaxged with the 
fluctuations of the KM.F, 



Tlie effeetiM retirtanee of a circuit to an alternating currant depends 
on the shape of the circuit, the specific resistance, permeabihty. enm 
section and shape of the conductor, and the frequency of the current. Tne 
current density over the cross section of the conductor is a minimum at 
the center, increasing to a maximum at the periphery; in a solid ocmductor 
of large cross section the current is confined almost entirely to an outer 
shell or "skm." The *'Skin Effect Factor" is the number by wUdi the re- 
sistance of the circuit to a continuous current must be multiplied to give 
the effective resistance to an alternating current. The following curv^ 
formula and table give the "Skin Effect Factor" for a straight wire of 
circular cross section, the return wire of the drcuit being assumed suffi- 
ciently remote to be without effect, which is practically the case in an 
a&ial transmission line. 

Let R mm Resistance of wire In ohms to a continuous eurrsnt. 

R* >« Effective resistance of wire in ohms to an alternating current. 
/ >« Cycles per second. 
A ■" C^ces section of wire in circular mils, 
fi — Permeability of wire in O.G.S. units. 
< — Temperature in ®C. 
a -■ Temperature coeffident per ^G. 

C ■■ Percentage conductivity of wire referred to Biatthi assent 
copper standard at 0" 0. 

Then B'.toetionof (|!|^,). 

This function is a complex one, and can be represmted best by the 
accompanying curve; however, for 

{^>3X10W. 

R* I fp^CA 

the approximate formula -^ — 10~*y Yt:^"+0.28 

is sufficiently accurate for all practicable purposes. 

286 



SKIN SrFBCI FACTORS. 



mtm ■«*•« rmetmtm m* MK O. tmr MnUfM W^lM* Ba*iar 



Pioduotofar- p,^ 


ar*lbT 


ProduetofCii- 


rMtorfor 


tXA. ' 


■uo. 


Cydi^J*^ Co^ 


'00 " 


■>Ji' 


— Sooiooo 




fi,000.000 1 


■ooo~ 


.000 


i.ooa.000 




10,000,000 1 




.000 


2,000.000 


0«8 


20,000,000 1 




.000 


s.000.000 


IM 


ao.000.000 1 






4MO.00O 




40.000.COO 1 






UODOOO 


333 


50.000,000 1 






ftOOO.000 














70,000,000 1 


12« 








80 


»o,ooo 


158 


!ow 






M 




IBS 


.OSS 




785 




vo.tm 




.104 




974 


IM 


XX),000 










ISO 








iTjsooiooo 










:2eo 


a».ooo.ooo 


42 


200 






.330 


26.000.000 


B8 


260 




790 


.46e 


30.ODO.aOO 




30C 




037 


.570 












.680 




31 


40C 




20 


.737 


4M)00.000 


40 


4SC 


000,000 


31 




sajmjooa 






XJO.OOO 




!oe5 


S6M0m 


S3 




oooioSo a 




-06 




» 


600 




6S 


.18 



i 



' Thk corrMpondi to E.B.B. Mesnph wire. 



TRANSMISSION CIRCUITS. 



267 



mf 



C« 



per IV^lrtt per lOOO 



M< Im Am 
drcnn 

■ BXTWKSN WiRss, E" 10,000 VoLTB. Frbqubnct, / — 26 CrcLBS 

PBR SSCOND. 
Ca^BOINa CUBBJBNT PBB WtBB — 1.815 C. 

NoTK. — Values of chars^ing current at other pressures are proportional 
to those given in this table. 



Interazial Distances. 



Dia. 

over 
Insai. 




I' 



01358 
.01312 
.01263 
.01214 
.01167 
.01230 
.01138 
.01001 
.01045 
.01073 
.00082 
,00006 
.00833 



.01083 
.01002 
.00800 
.00768 
.00690 
.00624 



.01132 
.00967 
.00900 
.00844 
.00748 
.00671 
.00610 
.00559 



Y 



.01299 
.01183 
.01085 
.01004 
.00933 
.00871 
.00769 
.00728 
.00690 
.00624 
.00670 
.00523 
.00486 



1' 



.01044 
.00069 
.00902 
.00844 
.00793 
.00740 
.00673 
.00641 
.00610 
.00559 
.00515 
.00479 
.00446 



.00710 
.00673 
.00641 
.00612 
.00584 
.00559 
.00515 
.00497 
.00479 
.00446 
.00417 
.00394 
.00372 



8' 



.00597 
.00572 
.00548 
.00526 
.00606 
.00488 
.00454 
.00430 
.00425 
.00309 
.00876 
.00856 
.00337 



6' 



.00470 
.00454 
.00439 
.00425 
.00412 
.00399 
.00377 
.00367 
.00856 
.00337 
.00821 
.00307 
.00294 



12* 



.00388] 
.00377 
.00367 
.00367 
.00347 
.00337 
.00321 
.00314 
.00307 
.00294 
.00281 
.00260 
.00259 



18' 



.00852 
.00843 
.00834 
.00327 
.00318 
.00310 
.00296 
.00290 
.00283 
.00272 
.00261 
.00252 
.00243 



Sue Cir. Mils 






Interaxial Distances. 






Stranded. 


6' 


12* 


18' 


24' 


36' 


48' 


60* 


72* 


14)00.000 
000,000 
SOO.OOU 
750000 
7O04X)O 

eooxxK) 
fioaooo 

450.000 

4oaooo 

350.000 

300.000 

260.000 

0000 

000 

00 



1 

3 
4 . 

Solid 

Solid 8 

Solid 10 


.00055 
.00641 
.00626 
.00617 
.00608 
.00590 
.00570 
.00559 
.00548 
.00535 
.00521 
.00504 
.00492 
.00474 
.00457 
.00443 
.00426 
.00412 
.00388 
.00356 
.00337 
.00321 


.00506 
.00497 
.00488 
.00483 
.00506 
.00466 
.00454 
.00446 
.00439 
.00430 
.00421 
.00410 
.00403 
.00390 
.00379 
.00368 
.00357 
.00348 
.00330 
.00307 
.00^4 
.002dl 


.00446 
.00439 
.00432 
.00428 
.00423 
.00416 
.00405 
.00399 
.00392 
.00386 
.00379 
.00376 
.00363 
.00354 
.00345 
.00336 
.00327 
.00318 
.00303 
.00283 
.00272 
.00261 


.00412 
.00405 
.00399 
.00396 
.00392 
.00385 
.00376 
.00372 
.00367 
.00361 
.00354 
.00347 
.00341 
.00332 
.00323 
.00316 
.00308 
.00299 
.00287 
.00269 
.00259 
.00249 


.00370 
.00367 
.00361 
.00859 
.00856 
.00350 
.00343 
.00337 
.00334 
.00328 
.00323 
.00318 
.00312 
.00305 
.00298 
.00292 
.00285 
.00278 
.00267 
.00252 
.00241 
.00234 


.00847 
.00343 
.00337 
.00336 
.00334 
.00328 
.00321 
.00318 
.00314 
.00310 
.00305 
.00299 
.00296 
.00288 
.00283 
.00276 
.00270 
.00265 
.00254 
^239 
.00232 
.00223 


.00330 
.00827 
.00323 
.00321 
.00318 
.00312 
.00307 
.00805 
.00301 
.00296 
.00292 
.00287 
.00283 
.00278 
.00270 
.00267 
.00259 
.00254 
.00245 
.00232 
.00225 
.00218 


.00318 
.00314 
.00310 
.00308 
.00307 
.00301 
.00296 
.00294 
.00290 
.00287 
.00283 
.00278 
.00274 
.00289 
.00263 
.00258 
.00252 
.00247 
.00238 
.00227 
.00218 
.00212 



ALTEBKATINO CURBBNT CIRCUITS. 



259 



ja,e tntp^nee («) of a circuit is defined aa the ratio of the difference in 
preasure (^ective) between the two ends of the conductor to the current 
^*%Sp'*I?},™^°8 through the conductor. , 

The £.M.F. required to overcome impedance is 



In the case of direct currents « — r. 

The following are typical altonating current circuits: 

B *■ resistance in ohms. 
Z -• impedance. 

• — 2 ir/. 

L — coefficient of sdf induction. 
C ■» capacity. 



or diacrminmaitieaUy, 



and I»dactaMC«, In 




( 



Fio. 12. 



and Capadtar li 




Fxa. 13. 



Jic«, XndnctoBC*, and Capacitj li 



or di^fti a mmat ically, 




Nors-T-Intiunsausaion hnes the capacity is m parallel with the reaist- 
anee and mductance; the above formula mvolving capacity do not there- 
fore apply. For the discussion of capacity of transmission lines see p 264. 



260 CONDUCTORS. 



THE DIMENSIONS OP CONDUCTORS FOB 
DISTRIBUTION SYSTEMS. 

Bt Harold Pendeb. Ph.D. 

To proportion properly the sise of the conductors for a distributioo 
■ystem. the following data with res&rd to each circuit ia necessary: 

1. The nM»-yimiim power to be transmitted, or the maTimiiTn load on the 

line. 

2. The load factor, or the variation of the power delivwed with tima. 
8. The length of the line. 

4. The distribution of the load alon^^ the line. 

5. The pressure at which the power is to be transmitted. 

6. The loss of power which may be allowed in the line. 

lliese six ooncfitions will determine a conductor of a definite cross sec- 
tion, but no conductor should ever be used which is not of sufficient siae 
both to insure the proper mechanical strength and also to prevent a dan- 
gerous temperature elevation; the first condition is of particular impc»^ 
tance in overhead lines, the second in underground and interior wiring. 

Assuming that the amount and distribution of the load and the timnt- 
mission distance are known, the engineer has next to determine, what line 
pressure to employ and wliat power loss to allow. To do this, he must 
keep in mind two fundamental facts, namely, that the transmission syatem 
is but part of the entire plant, and that the object of the plant as a whole 
is to gain the maximum net revenue for the least expenditure of money; 
also, that there is usually a limit to the capital available for the enter- 
prise, which the first cost of the entire plant must not exceed, even thou^ 
a further increase of the capital outlay might gain a desirable revenue. 
Consequently, in the selection of the pressure and efficiency for a distribu- 
tion system, many complex factors enter, such as the nature of 
the supply ot energy, the nature of the load supplied, the probability of 
increase in the demand for power, etc., as well as the relative costs of the 
various parts of the plant. Space does not permit of a detailed discus- 
sion of all these factors here; it will suffice to state briefly the general Amer- 
ican practice under the most common ocMiditions. 

XIME PREAHURS. — To transmit a given amount of power a givioi 
distance at a fixed efficiency, the amount of copper required will vary 
inversely as the square of toe pressure. High pressure then means de> 
crease in the cost of the conducting material, but an increase in the cost 
of insulating the line and the rest of the system. As a general rule, espe- 
cially in long distance transmission, the saving in copper as the pressure 
is increased more than offsets the increased cost of insulation, up to about 
60,000 volts, but in many cases other factors fix a much lower economical 
limit to the line pressure. Recent improvements in the design of insula- 
tors accompanied by a decrease cost of manufacture have raised the 
economic limit of line pressure to 100,000 volts. 

Direct Current jDtstrlbatlon. — On direct current systons supply- 
ing directly incandescent lamps and small motors, the maximum pressure 
allowable is 125 volts for two-wire distribution, 250 volts for three-wire 
distribution; in certain cases where cheap power may be had, these figures 
may be increased to 250 and 600 respectively. For large direct ctirrent 
motor systems the corresponding figures are 500 to 600 volts for two-wire 
and lOOiO to 1200 volts for three-wire ssrstems. The limiting transmisnon 
pressure is fixed by the maximum pressure which can be employed on the 
various translating devices, motors, lamps, and the like. Future devd- 
opments in the latter may set a new limit tp the allowable pressure; in 
fact, the compensating pole direct current motors now being placed on the 
market will permit the use of pressure as high as 1200 volts for two-wire 
and 2400 volts for three-wire systems. On circuits supplying direct cur- 
rent series arc lamps, pressures as high as 5000 volts are used. 



^ 



DIMENSIONS OF OONDUCTOBS. 261 



AHmwwkaMng Current IMsteflNitioB* — The line pressure on thftt 
part of an altematins current distribution system connected directly to 
the various tranriating devices, motors, lamps, and the like, is fixed by 
the practicable pressure that mav be used on these devices. For direct 
distnbution for incandesoent lignting, the tine pressure between wtres 
ihoukl not exceed 125 volts, or poesubly 260 volts if power is cheap and 
220 to 2dO vdit incandescent lamps can be advantageously employed. 

IHstrllbattoB l» Glttew. — In the larger cities the tendeney of modem 
pcmetios (1907) is to generate three-phase alternating current at 11,000 
or 13i000 volts (delta), and to transmit the power at this pressure either 
U> fltatie transformer or rotary converter substations. For the dia- 
tribution of direct current from rotary converter sub-stations see above 
ondcr "line Pressure for Direct Current Distribution." At the statio 
tnniformer sub-etatione the pressure is reduced to 2200 volts, and the 
power tranamitted at this pressure to the centers of distribution, where 
BaoUi«r reduction in pressure to about 125 or 260 volts takes place, and 
firam here tlM energy is distributed directly to the lamps, motors, or 
other translating device. In smaller dties, or when it is desired to employ 
overhead lines entirely (mnoe 11,000 volts overhead in cities is not advis- 
able), the sub-stations may be omitted and generators for 2200 volts be 
OMd. Large induction motors may be suppued directly with 2200 volt 
curren t, the very largest sometimes with current at 11.000 or 13,000 volts. 
POfrSlK XiOM M THS ULM A. — To transmit a given amount 
of power a given distance at a given pressure, the amount of copper 
rsqoired wilTvary inversely as the amount of power lost in transmission. 
Low effideney, therefore, means decrease in the cost of the conducting 
material, but an increase in the central station output. 

KAlvta'a Iiiftvr. — In genual, if two quantities A and B are both funo- 
tioof of the same variable x, then the sum of A + B is a minimum when 
tiie rate of change of A with respect to that variable is equal and opposite 
to ths rate of change of B with req>ect to that variable, i.e., when 

dA dB 

dx dx 

Numerous attempts have been made to apply this law to the determi- 
uukn of the most economical efficiency for a transmission line. At first 
a^t it would seem logical to proportion the costs of the central station 
ud ttaasmismlon line so that the annual cost of delivering an additional 
kilowatt of power by increasing the central station capacity will equal the 
*Biam\ cost of denvering an additional kilowatt of power bv adding 
OMe copper to the line. On this basis a very simple law is found to hold, 
o>ndy, that the most economical current density per million circular 
inileiB* 



880 



v/g- 



vhtte K* M increase in annual charges on transmission line, resulting 
from inereasing the weight of copper oAe ton (1^)00 lbs.). &nd Kp *" increase 
m annual operating and capital charges on the central station, resulting from 
inoeastng; the output one kilowatt. 

rlj ^^* ^vcver, is true only for a given current; when the power sup- 
^fn by any plant, and therefore the current, varies over wide Umits 
^viqg the year, as is almost invariably the case, the current density as 
^f^^naaed by the above law refers to the square root of the mean square 
^v^t for the year, a quantity which can be determined only to the 
'^''VBeet approximation. 

Farther, the whole disciission of economical cross section is based on 
two aasiimptions, usually unwarranted, namely, that the amount of capital 
Avauable ia unlimited, and that a market can be found for the maximum 
jvtput of the plant; it will evidently not be economical to install copper 
to aave power which cannot be sold. In short, neither Kelvin's law nor 



* The formula for aluminum is 106 



v/^- 



( 



262 OOKDUCTOBS. 



any modifioatton of it is a safe general guide in determining the proper 
allowance for leas of power in the line. Each plant has to be oonaiderad 
on its individual merits, and VariouB oonditione are likely to determine 
thepreasure and loss in different cases. 

MMmMhmtk^m JDIroct to Xnuulatanir Devtoee. — The power lorn 
in a tranamission line also fixes the pressure loss or volts drop. In direct 
current systems the per cent power loss equals the per cent pressure loss; 
in an alternating current line there is also a fixed relation between the two, 
see page 264. In that part of a distribution system connected directly 
to the translating devices, lamps, motors, etc., the regulation of the line, 
or the percentage pressure loss, must not exceed a certain amount oon* 
sistent with reasonably ^dent operation of these translating devices. 
For example, the maximum variation in pressure on incandescent lanqis 
should not be more than 2 per cent; distribution lines which supply incan- 
descent lamps and on which the pressure at the sending end is fixed, 
should thereifore be of sufficient sise to insure a pressure loss of not over 2 
per cent at maximum load. When a line supplies a large number of Istmpa, 
all of which are not likely to be burning simultaneously, the per cent drop 
in pressure for the connected load may be taken considerably greater. 
For example, if the probable maximum load be figured at one third of 
the connected load, a drop of 6 per cent for all lamps burning may be 
allowed. 

matiil»«tton in Ctonen^l. — The followinc discussion of the proper 

?Dwer loss to allow in transmission lines is taken from Bell, "£3ectrie 
6wer Transmission." 

" The commonest cases which arise are as follows, arranged in order of 
their frequency as occurring in American practice. Ekich case requires a 
s. mewhat different treatment in the matter of line loss, And the whole 
classification is the result not of a priori reasoning but of the study of a 
very large number of concrete cases. 

Cask I. General distribution of power and light from water-power. 
This includes something like two thirds of all the power transmission 
enterprises. The cases which have been investigated by the author have 
ranged from 100 to 20,000 H.P., to be transmitted all the way from one to 
one hundred and fifty miles. The market for power and light is usually 
uncertain, the proposition of power to light imknown within wide limits, 
and the total amount required only to be determined by future oonditionk. 
The average load defies even approximate estimation, and as a rule even 
when the general character of the market is most carefully investigated 
little certamty is gained. 

For one without the gift of prophecy the attempt to figure the fine for 
such a transmission by following any canonical nues for maximum econ- 
omy is merely the wildest sort of guesswork. The safest process is as fol- 
lows: Assume an amount of power to be transmitted which can certainly 
be disposed of. Figure the hne for an assumed loss of energy at full load 
small enough to insure good and easy regulation, which determines the 
quality of the service, and hence, in large measure, its ^p^wth. Arrange 
both power station and line with reference to subsequent increase if needed. 
The exact line loss assumed is more a result of trained iudgment than of 
formal calculation. It will be in general between 5 and 16 per cent, for 
which losses eeneratorc can be conveniently regulated. If raising and 
lowering transformers ore used the losses of ener^^y in them should oe in- 
cluded m tiie estimate for total loss in the line. In this case the loss in the 
line proper should seldom exceed 10 per cent. A loss of less than 5 per 
cent 18 sddom advisable. 

It should not be forgotten that in an alternating circuit two small con- 
ductors are generally better than one large one, so that the labor of in- 
stallation often will not be increased by waiting for developments before 
adding to the line. It frequently happenn, too, that it is verjr necessary 
to keep down the first cost of installation, to lessen the financial burden 
during the early stages of a plant's development. 

Cass II. Delivery of a known amount of power from ample water- 
power. This condition frequently arises in connection with manulactur- 
ing establishments. A water-power is bought or leased in toto, and the 

Sroblem consists of transmitting sufficient power for the comparativdy 
xed needs of the works. The total amount is generally not laige, seldom 



DIXSKSIOKS OF C0NDUCT0B8. 263 



tfaaii a few hundred hone-power. Under these ciroumstanoee the 
diottld be derigned for minimum fini coat, had any loss in the line 
'Ue that does not lower the efflcienoy^enough to force the ubc 
IMS of dynamos and water-wheels. These nses almost invari- 
•re near *»^»Fg** toKether to involve no trouble in regulation if the 
be chw deaopied. The operatijctf eTpense beoomes practically a fixed 
fB io that the first cost only need be considered. 
Sen phats are increasingly common. A brief trial calculation will 
ov St once the conditions of economy and the way to meet them. 
CissllL Dehwy of a known power from a closely limited source, 
ease resembles the last, except that there is a definite limit set for the 
mtfae system. Instead, then, of fixing a loss in the line based on regu- 
and first cost alone, the first necessity is to deliver the re9uired 
This may call for a line more expensive than would be indicated 
•By of the formuls for maximum economy, since it is far more impor- 
to avoid a siyplementary steam plant entirdy than to escape a con- 
ible increase in cost of line. The data to be seriously considered are 
COM of maintaining such a supplemoatary plant properly capitalised, 
theprioe of the aoditional copper that render it unnecessary. Maxi- 
' flficiency is here the governing factor. In cases where the motive- 
is rented or derived from steam, formulas like Kelvin's may some- 
be eonve&ient. Losses in the line will often be as low as 5 per cent, 
isMs only 2 or 3. 
Ciss rv. lAstribution of ]x>wer in known amount and units, with or 
^^tboQt long distance transmission, with motive-power which, like steam 
tetted water-power costs a certain amount per horse-power. Here the 
idmtiim is minimum cost per H.P., and design for this purpose may 
euiied oat with fair accuracy. Small line loss is generally desirable 
the systenx is complicated by a long transmission. Such problems 
/ w often appear as distributions only. Where electric motors are 
enpetition with distribution by shafting, rope transmission, and the 
' 2 to 5 per cent line loes may advantageously be used in a trial oom- 

Tbe problem of power transmisson may arise in still other forms than 
inst mentioned. Those are, however, the commonest types, and are 
"^ to show how completely the point of view has to cnange when 
. . ^ Ji^^ta under various dreumstanoes. The controlling element 
.■tf be minimum first oost, maximum efficiency, minimum cost of trans- 
' I, or eombinations oi any one of these, with locally fixed require- 
as to one or more of the others, or as to special conditions quite apart 
aayof them. 
a T«ry many cases it is absolutely n e c essa ry to keep down the initial 
*Mt, eren at a considerable sacrifice in other re^>ects. Or economy in a 
*^Ks ffireetion must be sbught, even at a considerable expense in some 
*^ direetion. For these reasons no rigid system can be followed, and 
y* »i eoostant nece s si ty for individual skill and judgment. It is no 
**<MD>noQ thing to find two plants for transmitting equal powers over 
*w ame distance under very similar conditions, which must, nowever. be 
"WN Psd on totally different plans in order to best meet the requirements.'' 




264 00NDUCT0B8. 



Let 



CAMXJUMJLTMON OF TRAIVSIHIASKOM UOTBft. 

Harold Pbndbr, Ph.D. 



E — pressure between adjacent wires at receiving end in volts. 

W « power delivered in kilowatta. 

k a- power factor of the locui expressed as a decimal fraction. 

A — cross section of each wire in millions of cireular mils. 

w -a total weight of conductors in pounds. 

{ <* length of cireuit (length of each wire) in feet. 

R ■■ resistance of each wire in ohms. 

U a" reactance factor of line ■■ ratio of line reactance to line resiatanes 

(Table II). 
Q ■> per cent power loss in terms of delivered povrer. 
P » per cent pressure drop in terms of delivered pressure. 



Put 
F 



IW 
{kEV 



In Table I are given formule for calculating the cross section, weight, 
and power loss for any kind of conductor. The per cent pressure drop, /*, 
can be readily calculated when the per cent power loss is known by means 
of the formula 

Where M and N are oonstants depending on the power factor (7;) and the 
ratio tt of the line reactance to the line resistance, this ratio is called the 
"reactanoe-f actor"; Tables III and IV rive the values of the constants M 
and N for various values of k and (i. To a dose approzunation. ezospt 
when the power factor is nearly unity, or the receiver current is leading, the 
term NQ^ mtiy be nM^leoted. i.e.. in most practical cases P -■ MQ, The 
complete expression P'^ MQ 4- NQ* ia exact in all eases for a 10 per cent 
power loss; it is in error less than 3 per cent for any value of P less than SO; 
m any case likely to arise in practice the discrepancy is less tlum 1 per cent 
in the value of P. The exact expression for P in terms of Q is 

P - Vi04 + 200 (1 + tt'bcHi + (1 + <i») kHi^ - 100 
where I is the tangent corresponding to the oosine k. (See p. 276.) 



Effect •r I^tne G»pttcMj. 

The effect of the capacity of the line b to reduce the pressure drop, i.e., 
improve the regulation, and to decrease or increase the power loss depend- 
ing on the load and ix>wer factor of the receiver. Let 

6 - 2 ir/C X 10-«. 

Where C is the capacity of the condenser in microfarads formed by any pair 
of wires of the line, f is the fre9uency; 6 is called the capacity susceptance 
of the line (for a single-phase line, the charging current is ba; for a three- 
phase line the charging current per wire is 1.155 bE. 

Table V gives the values of the capacity susceptance per 1000 feet of 
cireuit for various sises of wire spaced various distances ajpart for a frequency 
of 100 cycles per second; the values for other frequencies are directly pro- 
portional. (Continued on p. 270.) 



CAtCDLATlOV or TKAK8MIBSION LINES. 









1 


3 




fell 


i 


1 

! 


t* 


r 


i» 


S 




i 




li 


3 o 


z 


3 
S 






1 




8 o 




S 


8 r 


fell 
V 


s 


i 




b, 


K 


3 
S 




i 


I 

S 


ifclii 


^ 1 
8lo 


=u 


3 
S 


S -! 


1 
f 






J 


» 


9 


i 




1 
1 


II 


1 

i 
If 

-■■3 


I; 
h 

■Mi 

& 


fei 

ii 


6 

1 

1 



CALCULATION OF TBAN8MISSI0N LINES. 



267 



Tabto lUL— Valm 





Power Factors of Receiver. 


Raactanoe 
Fketon. 


Current Leading. 


Current Lagging. 


tt- 


90 


95 


98 


100 


98 


95 


90 


85 


80 


70 


0.0 
0.1 
0.2 


.81 
.77 
.73 


.90 
.87 
.84 


.96 
.94 
.92 


1.00 
1.00 
1.00 


.05 

.98 

1.00 


.90 
.93 
.96 


.81 
.85 
.89 


.72 
.76 
.81 


.64 
.69 

.74 


.49 
.54 
.59 


0.3 
0.4 
0.5 


.60 
.65 
.61 


.81 
.78 
.75 


.90 
.88 
.86 


1.00 
1.00 
1.00 


1.02 
1.04 
1.06 


.99 
1.02 
1.05 


.93 

.97 

1.01 


.86 
.00 
.94 


.79 
.83 

.88 


.64 
.60 
.74 


0.6 
0.7 
0.8 


.64 

.60 


.72 
.69 
.66 


.84 
.82 
.80 


1.00 
1.00 
1.00 


1.08 
1.10 
1.12 


1.08 
1.11 
1.14 


1.05 
1.09 
1.13 


.99 
1.08 
1.08 


.93 

.98 

1.02 


.79 
.84 
.89 


0.9 
1.0 
1.1 


.46 
.42 
.38 


.63 
.61 
.58 


.78 
.77 
.76 


1.00 
1.00 
1.00 


1.14 
1.16 
1.18 


1.17 
1.20 
1.23 


1.17 

1.20 

.1.24 


1.13 
1.17 
1.21 


1.07 
1.12 
1.17 


.04 

.90 

1.04 


1.2 
1.3 
1.4 


.84 
.80 
.26 


.55 
.52 
.40 


.73 
.71 
.69 


1.00 
1.00 
1.00 


1.19 
1.21 
1.23 


1.26 
1.20 
1.32 


1.28 
1.32 
1.36 


1.20 
1.31 
1.35 


1.22 
1.27 
1.31 


1.09 
1.14 
1.10 


1.5 
1.0 
1.7 


.22 
.18 
.14 


.46 
.43 
.40 


.67 
.65 
.63 


1.00 
1.00 
1.00 


1.25 
1.27 
1.29 


1.35 
1.38 
1.41 


1.40 
1.44 
1.48 


1.39 
1.44 
1.48 


1.36 
1.41 
1.46 


1.24 
1.29 
1.34 


1.8 
1.0 
2.0 


.10 
.07 
.03 


.37 
.34 
.31 


.61 
.59 
.57 


1.00 
1.00 
1.00 


1.31 
1.33 
1.35 


1.44 
1.47 
1.50 


1.51 
1.56 
1.59 


1.53 
1.58 
1.62 


1.50 
1.55 
1.60 


1.39 
1.44 
1.49 


2.1 
2.2 
2.3 


-.01 
-.00 


.28 
.25 
.22 


.55 
.53 
.61 


1.00 
1.00 
1.00 


1.37 
1.39 
1.41 


1.53 
1.56 
1.50 


1.63 
1.67 
1.71 


1.66 
1.70 
1.75 


1.65 
1.70 
1.75 


1.54 
1.59 
1.64 


2.4 

2.5 

2.0 


-.13 
-.17 
-.21 


.19 
.16 
.13 


.40 
.47 
.45 


1.00 
1.00 
1.00 


1.43 
1.45 
1.47 


1.62 
1.64 
1.67 


1.75 
1.79 
1.83 


1.80 
1.84 
1.88 


1.79 
1.84 
1.89 


1.69 
1.74 
1.79 


2.7 
2.8 
2.9 


-.25 
-.29 
-.33 


.30 
.07 
.04 


.43 
.41 
.39 


1.00 
1.00 
1.00 


1.49 
1.61 
1.53 


1.70 
1.73 
1.76 


1.87 
1.91 
1.96 


1.93 
1.98 
2.02 


1.94 
1.98 
2.08 


1.84 
1.89 
1.94 


3.0 
3.1 
3.2 


-.36 
-.40 
-.44 


-.01 
-.02 
-.06 


.37 
.36 
.34 


1.00 
1.00 
1.00 


1.55 
1.57 
1.58 


1.79 
1.82 
1.85 


1.99 
2.08 
2.04 


2.06 
2.11 
2.15 


2.08 
2.13 
2.18 


1.99 
2.04 
2.09 


3.3 
3.4 
3.5 


-.48 
-.62 
-.56 


-.08 
-.11 
-.14 


.32 
.30 
.28 


1.00 
1.00 
1.00 


1.60 
1.62 
1.64 


1.88 
1.91 
1.94 


2.10 
2.14 
2.18 


2.20 
2.24 
2.29 


2.23 
2.27 
2.32 


2.14 
2.19 
2.24 




i 



268 



OONDUCTOKS. 



Tal*l« IV.-~Val««* of M. 





Power Factors of Receiver. 


Reactance 
Factors. 


Current Leading. 


Current Lagging. 


h- 


90 


95 


98 


100 


98 


95 


90 


86 


80 


70 


0.0 
0.1 
0.2 


.001 
.001 
.002 


.001 
.001 
.001 


.000 
.000 
.001 


.000 
.000 
.000 


.000 
.000 
.000 


.001 
.000 
.000 


.001 
.000 
.000 


.001 
.001 
.001 


.001 

001 

.001 


^062 
.001 
.001 


0.3 
0.4 
0.6 


.002 
.003 
.003 


.002 
.002 
.003 


.001 
.002 
.002 


.000 
.001 
.001 


.000 
.000 
.000 


.000 

.000 

000 


.000 
.000 
.000 


.000 
.000 
.000 


.000 
.000 
.000 


.001 
.000 
.OUU 


0.6 
0.7 
0.8 


.003 
.004 
.005 


.003 
.004 
.005 


.003 
.004 
.005 


.002 
.002 
.003 


.000 
.001 
.001 


.000 
.000 
.001 


.000 
.000 
.000 


."boo 

.000 
.000 


.000 
.000 
.000 


.000 

Am 

.000 


0.9 
1.0 
1.1 


.006 
.007 
.008 


.006 
.006 
.007 


.006 

.008 

..007 


.004 
.005 
.006 


.002 
.002 
.003 


.001 
.002 
.002 


.001 
.001 
.001 


.000 
.001 
.001 


.000 
.000 
.000 


.000 
.000 

.ouo 


1.2 
1.3 

1.4 


.009 
.010 
.011 


.008 
.010 
.011 


.008 
.009 
.011 


.007 
.008 
.009 


.004 
.005 
.006 


.003 
.003 
.004 


.002 
.002 
.003 


.001 
.001 
.001 


.000 
.000 
.001 


.000 
.000 
.000 


1.6 
1.6 
1.7 


.013 
.014 
.016 


.013 

*.014 

.016 


.012 
.014 
.015 


.010 
.011 
.013 


.007 
.008 
.009 


.005 
.006 
.007 


.003 
.004 
.004 


.002 

.002 

003 


.001 
.001 
.002 


.000 
.000 
.000 


1.8 
1.9 
2.0 


.017 
.018 
.020 


.018 
.019 
.021 


.017 
.019 
.021 


.015 
.016 
.018 


.011 
.012 
.013 


.009 
.010 


.005 
.006 
.006 


.003 
.003 
.004 


.002 
.002 
.003 


.000 
.000 
.001 


2.1 
2.2 
2.3 


.022 
.023 
.025 


.023 
.025 
.027 


.023 
.02r> 
.027 


.020 
.022 
.024 


.015 
.016 
.017 


.011 
.012 
.014 


.007 
.008 
.009 


.005 
.006 
.006 


.003 
.003 
.004 


.001 
.001 
.002 


2.4 
2.6 
2.6 


.027 
.029 
.032 


.029 
.031 
.034 


.030 
.032 
.034 


.026 
.028 
.030 


.019 
.021 
.023 


.015 
.017 
.018 


.010 
.011 
.012 


.007 
.008 
.009 


.005 
.005 
.006 


.002 
.002 
.003 


2.7 
2.8 
2.9 


.(M4 
.036 
.038 


.036 
.039 
.041 


.037 
.040 
.042 


.033 
.035 
.037 


.024 
.026 
.028 


.020 
.021 
.023 


.013 
.015 
.016 


.010 
.010 
.011 


.006 
.007 
.008 


.003 
.003 
.004 


3.0 
3.1 
3.2 


.040 
.042 
.045 


.044 
.046 
.049 


.045 
.047 
.050 


.040 
.042 
.045 


.030 
.033 
.035 


.024 
.026 
.028 


.018 
.019 
.020 


.012 
.013 
.014 


.009 
.009 
.010 


.004 
.004 
.005 


3.3 
8.4 
3.6 


.048 
.051 
.053 


.052 
.055 
.059 


.053 
.056 
.060 


.048 
.051 
.054 


.038 
.040 
.043 


.030 
.032 
.034 


.021 
.023 
.024 


.015 
.017 
.018 


.011 
.012 
.013 


.005 
.006 
.006 



or TRAHSHISSIUN LINKS. 



ZSS 8|g SSS 



SSS 33S Si; 



s^^ sss sss s;gg gsi 



S3S 338 SSS 1 



;S5 ?3S nnS SS- 2~S S 



sti Wi^ l?i sp ii2 



270 



COKDUCTOBS. 



Using the same notation as given on page 264, putting H for the total 
rasistanoe and X ( — tiR) for the total reaotanoe of each leg of the fins^ 



Decrease in per) 
cent pressures p— 
drop ) 

Decrease in per) ^^ 
cent power loss j 



Single Phase. 



50 bX 



at - 



2kHi 



Three Phase. 



100 bJt 



2at - 



km 



where a «- 100 bR and ( is the tangent corresponding to the cosine k. (See - 
p. 276.) The true regulation of the line is then P — p, and the true per 
cent power loss is Q — q,P and Q being calculated by the formulae given 
on pages 264 and 265. These formulsB are approximate, being deduced on 
the assumption that the line oapBrcity can be represented by a condenser of 
half the capacity of the line shunted across the line at each end, but they 
are sufficiently accurate for any case likely to arise in practice. It is to be 
noted that the chan^ in regulation is independent of the load and the 
power factor, and is mdepenoent of the line resistance; the change in the 
per cent power loss varies with both the load and the power factor. 

IMrect Cmnremt, Tlu««* Wire B/mtmwi^. — Figure the wei^t and 
eross section of the outer conductors as if the middle or neutral wve was 
not present, putting E "- volts between outside wires. The neutral wire 
is usually taken from one-third to full sise of each outer conductor. The 
total weight of copper required will therefore be one-sixth to one-half 
greater than the weight determined by the above formula. 

Two-PIUMe, VQ«r« Wlr« System. — Treat each phase separately, 
remembering that half the power is delivered by each phase, and B * 
volts between diametrically opposite wires. 

Two-Pliflwe, Three- Wire Sjetem. — 



Let 
E 
V 



pressure between each outer and middle wire at receiving end in volts, 
pressure between each outer and middle wire at generating end in 

volts. 
Other symbols as above. 



Then for equal rise of temperature in the three conductors the following 
formtilsB hold. (The total weight of conductor required for this condition 
is only a fraction of one per cent greater than for the condition of maximum 
economy.) 





Copper. 

100 % conduc- 
tivity. 

20*» Centigrade 
or 68« P. 


Aluminum. 
62 % conduc- 
tivity. 
20*" Centigrade 

or68«F. 


Any Material. 
pB microhms 

per cu. in. 
6 — lbs. per 

cu. in. 


Cross section of each 

outer wire in million j4i -• 
CM* / 

Cross section of middle 1 j _ 
wire in milUon CM. }-*« 

Total weight in pounds w » 
Total weight in pounds v> = 


0.93F 


1.60F 


1.37pF 


Q 
1.26A, 

9.85Mi 
9A51F 


Q 
1.26^1 

2. 971 Ay 
AA51F 


Q 
1.26iii 

30.7«4i 
42.lpHF 


Q 


Q 


Q 



On the B. A S. sauge the middle wire is larger than each outer by one 
number (see p. 146;. 



HXTMBBICAIi BXAMPLEB OF CALCULATIONS. 271 



• mr si«re Clrealte In ggr t — . 



The above formalie and tables are also applicable to the ease of two or 
more drouite in series, i.e., a transmisaion line and transformer, if we put 

A ■■ Ri + R% 4* • • • • 

Btlt + R^ 

iHm Ai, A,, etc., are the resistances of the separate eireuits and tu h, etc. 
are the reactance factors of the separate drcuita. 



IMrect C«rmaty Vw«-¥Ftre Sjateaa. 

CoppsR WntBiL 

Gnm W ^ 40 kilowatts. 

E " 200 volts. 
2-500 feet. 
Q ■• 5 per cent, 

^*" ^^ — (20oF • 

Ch» section A - ^Q^^^'^ = 0.208 million CM. 

o 

The nearest commercial sise b No. 0000 B. db S. (see Table II) which has 
to area of 0. 212 million CM. 
Totol weight of copper w — 6.06 X 500 X 0.212 = 641 pounds. 

Power loss Q - ^ Q^^^g '^ - 4-»2 per cent. 

Prenure drop P »- Q "■ 4.92 per oent. 

Prenure at senerating end — 1 .0402 X 200 » 209.84 volts. 



{ 



Take tbe same constants as in the preceding case, considering E — 200 
volta as the pressure between outer wires. If the neutral wire is to be half 
ihe size of each outer, the total weight of copper required will be 

641 + ^-801 pounds. 

When the system is balanced there will be no current in the neutral wire 
and the r^ulation and efficiency will be the same as above. If one side 
(rf the 83rstem is ftilly loaded, and the other side not loaded at all, the volts 
(hop in tiie loaded outer will be the same as if the system was balanced, 
anoe the same current flows, and the volts drop in the neutral will be twice 
the drop in the outer (same current and double resistance); hence total drop 
will be 14.8 volts in 100 volts or 14.8 per oent. The power loss will also be 
14.8 per cent or 2.96 kilowatts. 



272 CONDUGTOIUS. 



Copper Wirxs Spacbd 3 Fbbt Apabt. 

QiTon _/ •> 25 cycles per second. 

IT - 600 kilowatU. 

E -i 10.000 Tolts. 

I - 45,000 feet. 

k i- 0.9, i.e., 00 per cent power factor. 
Q "■ 10 per cent. 

Th-n V - 45.000X500 ^ 

^*'*" ^ " (0.0 X lo.ooo)^ " ®-2^^- 

CitMfl section A - ^ ^ ^^^'^^^ - 0.0678 miUion CM. 

The nearest oommerdal siie is No. 2 B. & S. (Table II), which has an area 
ol 0.0664 nuUion CM. 

Total weight of oopper to « 6.06 X 45,000 X 0.0664 ^ 18.100 Ibe. 

1? * ^1 j^ 2.08X0.278 o ^1 

Exact power loss Q -• — ^ ^^^^ — — 8.71 per cent. 

Reactance factor i^ - ^^ - 0.36. (Table II). 

Therefore Af - 0.05 (Table III). 

N - 0.000. (Table IV). 

Then, neglecting the capacity of the line. 
Pressure drop P - 0.95 X 8.71 - 8.27 per cent. 

Pressure at generatmg end - 108.27 X 10,000- 10.827 volts. 

Vwo«Pliaa«, Three- Wire Ayateai. 

CopPBB WiBBS Spacbd 3 Fbbt Apabt. 

Given / "■ 25 cycles per second. 

Yr - 500 kilowatts. 
E » 10.000 volts. 
I - 45.000 feet. 

h — 0.9. i.e., 90 per cent power factor. 
Q >- 10 per cent. 
Then 

V - 45.000. X 500 _ J. 

(0.9X10,000)* "■ 

Cross section of outers At - "^ iq " 0.0259 million CJI. 

The nearest commercial sise is No. 6 B. & S. (Table II) which has an area 
of 0.0263 million CM. The middle wire must therefore be No. 5 B. A S. 

Total weight of copper w - 0.85 X 45,000 X 0.0263 - 11,600 lbs. 

1? * 1 r. 0^3 X0.278 . p- . 

Exact power loss Q — — K-Tji^ii^ "■ 0.87 per cent. 

U.UzOO 

The pressure loss will depend upon how the wires are arranged on the 
poles. As a first approximation for anv ordinary arrangement, the reao* 
tance of each phase can be considered the same as in a single phase S3«tem 
with wires of the same cross section as the outer, spaced a distance apart 
equal to that between each outer and the middle wire. 

From Table II the reactance factor of a No. 6 wire correspondiii( to a 
three-foot spacing and 25 cycles is 

• t. - ^-0.15. 
Whence Jf - 0.87. 



NUMERAL EXAMPLES OF CALCULATIONS. 273 

Th«n D«glectm« the eapeoity of the line, and uaing the approximate 
fofmula P ^ -Az V* 

gwirediop P - 9.87 X 0.87 - 8.69 per eent. 

rnoBure at gieneratins end — 1.0859 X 10,000 — 10,869 volte. 



I 



GoppBB WiBBS Spaced 6 Kbit Apast. 

Qiwi / i_ 60 cycles per aecond. 

W » 10,000 kilowatts. 
B - 60,000 volts. 
I - 400,000 feet. 

k — 0.86, i.e., 86 per cent power factor. 
Q » 12 per cent. 

^a^ J, _ 400.000 X 10.000 ^ 

(0.85 X 60,000>« •*^* 

Owi aeetion ^ - ^-^^ X1.04 ^ ^ ^^ ^^.^^ ^^ 

-^^JJS*'^* commercial size ib No. 00 (see Table II), which has an ana 
(10.133 milhon CJf. 

Total vdght of copper w - 9.09 - 400,000 X 0.133 X 484.0001b. 

Ntgltaing Kne eapacUy, 
Eaet power loss Q - ^'^^^'^ - 12 per cent. 

Beaetaoce factor «, -3.06x0.6-1.84. 

Tbewfore M - 1.55. 

^ N - 0.003. 

fttwiredrop P - 1.55 X 12 + [0.003 X (12)1 - 19.0. 

^M of U%B eapaeHy (see p. 204). 

b -.00000089X0.6x400-0.000214. 

(Table V). 

R -0.0778x400-31.1 (Table II). 

^j^^ X - 1.84 X 31.1 - 67.2. 

Dwwse in per oent preasure drop - p « lOO X 0.000214 x 57.2 - 1.2. 

a -100x0.000214X31.1-0.67. 
t - 0.62. 

DwBMsinperoent power loes-ff -2X0.67X0.62- ,-^^fP* ^ - 0.8. 

\U. ooj* X12 

Whence 

Jae presBiiPB drop - 19.0 - 1.2 - 17.8 per oent. 

jgqe p ower loss - 12.0 - 0.8 - 11.2 per cent. 

ntmazt at generatmg end - 1 . 112 X 60.000 - 66.720 volta. 




( 



274 



CONDUCrOHS. 



TRAJTsmssioiv uoRns OF Kirowir comstahva. 

The following formuUe and tables give an exact method of calculating 
the efficiency and regulation of a tranamiasion line of known conBtanis, 
in terms of the pressure between adjacent wires at the generating end of 
line. 



Given: 



The kind of system, direct or alternating, 



n — number of phases, for the ** single phase " system n -» 2. 
/ B frequency in cycles per second. 

V = pressure between adjacent wires at generating end, in volts. 
W » power delivered in watts. 
COS a ■■ power factor of load at receiving end. 
R -■ resistance of each wire in ohms. 
X = in ductive r eactance of each wire in ohms, 

, Z — \/R^-^ X^ — impedance of each wire. 

Required: E — pressure between adjacent wires at receiving end in volts. 
/ ■» current per wire in amperes. 
H •- total power lost in watts. 
The values of E, /, and H are given in the table on p. 275. For approx- 
imate calculations J can be taken equal to unity; the exact value of J is 
given in the table below. 



ITalnea of 9» 



e 


000 


.001 


.002 


.003 


.004 


.005 


.006 


.007 


.008 


.009 


.00 
.01 
.02 
.03 
.04 
.05 


1.0000 
1.0001 
1.0004 
1.0009 
1.0016 
1.0025 


1.0000 
1.0001 
1.0004 
1.0010 
1.0017 
1.0026 


1.0000 
1.0001 
1.0005 
1.0010 
1.0017 
1.0027 


1.0000 
1.0002 
1.0005 
1.0011 
1.0018 
1.0028 


1.0000 
1.0002 
1.0006 
1.0012 
1.0019 
1.0029 


1.0000 
1.0002 
1.0006 
1.0012 
1.0020 
1.0030 


1.0000 
1.0003 
1.0007 
1.0013 
1.0021 
1.0031 


1.0000 
1.0008 
1.0007 
1.0014 
1.0022 
1.0032 


1.0001 
1.0008 
1.0008 
1.0014 
1.0023 
1.0034 


1.0001 
1.0004 
1.0008 
1.0015 
1.0024 
1.0035 






.000 


.002 


.004 


.006 


.008 


« 


.000 


.002 


.004 


.006 


.008 


.06 


1.004 


1.004 


1.004 


1.004 


1.005 


.29 


1.102 


1.104 


1.106 


1.108 


1.110 


.07 


1.005 


1.005 


1.005 


1.006 


1.006 


.30 


1.111 


1.113 


1.115 


1.117 


1.119 


.08 


1.006 


1.007 


1.007 


1.007 


1.008 


.31 


1.121 


1.123 


1.125 


1.127 


1.129 


.09 


1.008 


1.008 


1.009 


1.009 


1.010 


.32 


1.131 


1.133 


1.135 


1.137 


1.139 


.10. 


1.010 


1.010 


1.011 


1.011 


1.011 


.33 


1.141 


1.143 


1.146 


1.149 


1.151 


.11 


1.012 


1.012 


1.013 


1.013 


1.014 


.34 


1.154 


1.166 


1.158 


1.161 


1.163 


.12 


1.014 


1.015 


1.015 


1.016 


1.017 


.35 


1.167 


1.169 


1.171 


1.174 


1.177 


.13 


1.018 


1.018 


1.019 


1.019 1.020 


.36 


1.180 


1.183 


1.186 


1.189 


1.192 


.14 


1.021 


1.021 


1.022 


1.022 1.023 


.37 


1.195 


1.199 


1.202 


1.206 


1.209 


.15 


1.024 


1.024 


1.025 


1.025| 1.026 


.38 


1.213 


1.216 


1.220 


1.224 


1.227 


.16 


1.027 


1.027 


1.028 


1. 02911. 030 


.39 


1.231 


1.234 


1.238 


1.242 


1.246 


.17 


1.031 


1.032 


1.032 


1.033,1.034 


.40 


1.250 


1.254 


1.258 


1.263 


1.267 


.18 


1.034 


1.035 


1.03G 


1.037 1.038 


.41 


1.272 


1.276 


1.280 


1.285 


1.280 


.19 


1.039 


1.040 


1.041 


1 .042 1 .043 


.42 


1.296 


1.301 


1.307 


1.312 


1.318 


.20 


1.044 


1.045 


1.046 


1.046 1.047 


.43 


1.324 


1.330 


1.336 


1.342 


1.349 


.21 


1.048 


1.049 


1.050 


1.051 1.052 


.44 


1.356 


1.363 


1.370 


1.377 


1.385 


.22 


1.053 


1.054 


1.056 


1.057 1.058! 


.45 


1.393 


1.401 


1.410 


1.409 


1.428 


.23 


1.059 


l.OGl 


1.062 


1.063 


1.06.5 


.46 


1.437 


1.447 


1.467 


1.468 


1.479 


.24 


1.066 


1.067 


1.068 


1.070 


1.071 


.47 


1.491 


1.504 


1.518 


1.632 


1.547 


.25 


1.072 


1.074 


1.075 


1.076 1.078 


.48 


1.563 


1.580 


1.599 


1.620 


1.643 


.26 


1.079 


1.081 


1.082 


1.083 1.084 


.49 


1.668 


1.697 


1.733 


1.778 


1.835 


.27 


1.086 
1.094 


1.087 
1.096 


1.089 
1.098 


1 .090 1 .092 


.50 


2.000 










.28 


1.099 


i.iool 











TRANSMISSION LINE OF KNOWN CONSTANTS. 275 



i 

! 

I « 



K} 



SI 
o 

5 

o 




^^>3 



a: 






feNfe 









8^ 






^ 



aq 



^ 



kl« 



Bq 



> -S 



|fiQ|S|fiQlS|flqiS|flqi'^J«il'> Wl*^ 









« 



0) 



ig 

QQ 



8fe 



Skit: 

oq .3 



"§ 



I 



I I 



+ 
05 



+ 



I 



I 

5. 



I 

03 
CI 

I 



s 

+ 

ft; 

I 



9 

+ 
ft; 

kl « 

a 

001 C 

I 



t 


s 


S 


8 


8 


8 


u 


U 


J" 




.fci 


c« 


^ 


^ 


^ 


^ 


^ 


^ 


e« 


a 


-* 


CO 


^ 


c 


1..? 


1 


J 


o 


1 


1 




t^ 


C4 


CO 


"♦ 


s: 






<0 

1 a 



1 1 

S I 

.9 ;: 

♦ S5 



( 



276 



OONDUCTOBS. 



i 


ValBM 


of taa a 


(= t) tn toi 


«•• 


f CM 


«(= 


k). 




C08« 


.000 


.002 


.004 


.006 


008 


ooea 
"k 

.50 


.000 


.002 


.004 


.006 


.008 


.00 




502 


250 


167 


125 


1.732 


1.722 


1.713 


1.704 


1.605 


.01 


166 


83.3 


71.4 


62.5 


55.4 


.51 


1.686 


1.677 


1.668 


1.650 


J -SI 


.02 


49.8 


45.4 


41.6 


38.5 


35.7 


.52 


1.642 


1.634 


1.625 


1.617 


1.600 


.03 


33.4 


31.2 


'29.4 


27.7 


26.3 


.53 


1.600 


1.592 


1.582 


1.574 


1.560^ 


.04 


24.9 


23.8 


22.8 


21.7 


20.8 


.54 


1.558 


1.550 


1.542 


1.534 


1.520 


.05 


20.0 


19.2 


18.5 


17.8 


17.2 


.55 


1.518 


1.510 


1.503 


1.494 


1.487 


.06 


16.6 


16.1 


15.6 


15.1 


14.7 


.56 


1.479 


1.471 


1.464 


1.456 


1.440 


.07 


14.2 


13.8 


13.5 


13.1 


12.8 


.57 


1.441 


1.434 


1.426 


1.419 


1.411 


.08 


12.5 


12.2 


11.9 


11.6 


11.3 


.58 


1.404 


1.397 


1.389 


1.383 


1.375 


.09 


11.1 


10.8 


10.6 


10.4 


10.2 


.59 


1.368 


1.361 


1.354 


1.347 


1.3« 


.10 


9.96 


9.76 


9.57 


9.38 


9.21 


.60 


1.333 


1.326 


1.319 


1.312 


1.306 


.11 


9.03 


8.87 


8.78 


8.56 


8.41 


.61 


1.299 


1.292 


1.285 


1.279 


1.27S 


.12 


8.26 


8.14 


8.01 


7.88 


7.75 


.62 


1.265 


1.258 


1.251 


1.246 


1.230 


.13 


7.63 


7.51 


7.40 


7.28 


7.18 


.63 


1.232 


1.226 


1.219 


1.213 


i.aoo 


.14 


7.07 


6.97 


6.87 


6.77 


6.68 


.64 


1.200 


1.194 


1.188 


1.181 


1.175 


.15 


6.59 


6.50 


6.41 


6.34 


6.25 


.65 


1.168 


1.162 


1.156 


1.150 


1.144 


.16 


6.17 


6.10 


6.02 


5.94 


5.87 


.66 


1.138 


1.132 


1.126 


1.119 


1.113 


.17 


5.80 


5.73 


5.66 


5.60 


5.53 


.67 


1.108 


1.102 


1.095 


1.09O 


1.084 


.18 


5.47 


5.40 


5.34 


5.28 


5.23 


.68 


1.078 


1.072 


1.066 


1.060 


1.055 


.19 


5.17 


5.11 


5.06 


5.00 


4.95 


.69 


1.048 


1.043 


1.037 


1.031 


1.02S 


.20 


4.90 


4.85 


4.80 


4.75 


4.70 


.70 


1.020 


1.014 


1.008 


1.002 


.998 


.21 


4.66 


4.61 


4.57 


4.52 


4.47 


.71. 


.992 


.986 


.080 


.976 


.070 


.22 


4.43 


4.39 


4.35 


4.31 


4.27 


.72 


.964 


.968 


.953 


.947 


.042 


.23 


4.23 


4.19 


4.15 


4.12 


4.08 


.73 


.936 


.031 


.925 


.920 


.014 


.24 


4.05 


4.01 


3.98 


3.94 


3.90 


.74 


.909 


.904 


.898 


.803 


.887 


.25 


3.87 


3.84 


3.81 


3.78 


3.75 


.75 


.882 


.876 


.871 


.866 


.861 


.28 


3.71 


3.68 


3.66 


3.62 


3.59 


.76 


.855 


.850 


.845 


.839 


.834 


.27 


3.57 


3.54 


3.51 


3.48 


3.46 


.77 


.829 


.823 


.818 


.813 


.807 


.28 


3.43 


3.40 


3.38 


3.35 


3.33 


.78 


.802 


.797 


.792 


.786 


.781 


.29 


3.30 


3.27 


3.25 


3.23 


3.20 


.79 


.776 


.771 


.765 


.760 


.755 


.30 


3.18 


3.16 


3.13 


3.11 


3.09 


.80 


.750 


.745 


.740 


.735 


.729 


.31 


3.07 


3.04 


3.02 


3.00 


2.98 


.81 


.724 


.719 


.714 


.708 


.703 


.32 


2.96 


2.94 


2.92 


2.90 


2.88 


.82 


.698 


.693 


.688 


.683 


.677 


.33 


2.86 


2.84 


2.82 


2.80 


2.79 


.83 


.672 


.667 


.661 


.656 


.651 


.34 


2.76 


2.76 


2.73 


2.71 


2.69 


.84 


.646 


.641 


.635 


.630 


.625 


.35 


2.68 


2.66 


2.64 


2.63 


2.61 


.85 


.620 


.614 


.609 


.604 


.598 


.36 


2.59 


2.58 


2.56 


2.54 


2.53 


.86 


.593 


.588 


.583 


.677 


.672 


.37 


2.51 


2.50 


2.48 


2.46 


2.45 


.87 


.667 


.562 


.556 


.651 


.545 


.38 


2.43 


2.42 


2.40 


2.39 


2.37 


.88 


.540 


.534 


.529 


.624 


.518 


.39 


2.36 


2.35 


2.33 


2.32 


2.31 


.89 


.512 


.507 


.601 


.496 


.490 


.40 


2.29 


2.28 


2.26 


2.25 


2.24 


.90 


.489 


.479 


.473 


.467 


.461 


.41 


2.23 


2.21 


2.20 


2.19 


2.17 


.91 


.456 


.450 


.444 


.438 


.432 


.42 


2.16 


2.15 


2.14 


2.12 


2.11 


.92 


.426 


.420 


.414 


.408 


.401 


.43 


2.10 


2.09 


2.08 


2.06 


2.05 


.93 


.395 


.389 


.383 


.376 


.370 


.44 


2.04 


2.03 


2.02 


2.01 


2.00 


.94 


.363 


.356 


.350 


.343 


.336 


.45 


1.98 


1.97 


1.96 


1 95 


1.94 


95 


.329 


.3M 


.314 


.307 


.290 


.46 


1.93 


1.92 


1.91 


1.90 


l.HO 


.96 


.292 


.284 


.276 


.268 


.259 


.47 


1.88 


1.87 


1.86 


1.85 


1.8t 


.97 


.251 


.242 


.232 


.223 


.213 


.48 


1.83 


1.82 


1.81 


1.80 


1.79 


.98 


.203 


.192 


.181 


.169 .156 


.49 


1.78 


1.77 


1.76 


1.75 


1.74 


1 .99 


.143 


.127 


.110 


.090 .063 



NoTa.— ThiB table is to be u^ed like a table of logarithms. e.g., the 
tangent corresponding to coe « ^^ .816 is .708. 



TRANSMISSION LINB CALCULATIONS. 277 



I When the tnoatadnc devices, whether lamps or motors, are scattered 
'~nier a ooosidenble area, the usual method of supplying them with power 
to ran a single feeder to some point near the ** center of gravity " of 
load, and from this center run out branches to feed groups of lunps or 
in paraUd. The center of gravity of the load can be readily deter- 
Bs follows: 

Let Wi, tPa, 10s, etc. 

icpresSDt the individual loads, 
i vkI Xi, za, X9, etc. 

: Bad Vu V% VH. etc., 

i icpresent the distances of these loads from any two fixed lines OX and OY 
! at ri^t anfl^es to eadi other. Then the center of gravity is that point which 
I k the distance 

_ ».«H +*">*+ **^+ ■■■ from OX 
mi r. - »'«H+«^+«^+-- from OY. 

I 

The center of gravity of the load is by no means always the most economl- 
I esl beation for the center of distribution, as considerations of the relative 
eoit of establishing the cent^ at this point in comjparison with the cost at 
oth« points, the probable change in the distribution of the load with the 
grovth of the system, etc., have all to be taken into account. 

The general scheme of feeders, centers of distribution, and branches 
caa be developed still further, and sub-centers, sub-feeders, etc., estab- 
fidied, until a point b reached where the saving in the cost of copper is 
hifiiiiwd by the increase in the cost cd the centers of distribution. 



CalcvlatloM at CrOM Section, W«lrliti *c. 

When a transmission line is loaded at more than one point, the conductor 
ihooki have such dimensions that the pressure drop at the end of the line, 
vhcn the line is supplsring the maximum load at each point, shall not exceed 
ft era amount. Whether the conductor shall be mode of uniform section 
thnndiout the length of the line, or be reduced in sise as the current 

» Muried diminishes, will depend on the r^tive amounts of energy su]^ 
pBed at, and the distances between, the various points at which the line is 
bide d. Below wiU be found formulsB for determining the weight and 
crasi ssetion of a line of uniform cross section, and hawng no returnee, 
■ipplyuig a distributed load. When the line has no inductive reactance 
the vei0^t and cross section of the conductor for a given pressure drop 

i ftre to a dose approximation independent of the power factor of the loads 
*t the various points. When the line has reactance, the formulse^ will mve 
only a first approximation to the correct weight and cross section. The 
nor invotved can bA determined by considenni^ each section of the line 
Mperateiy, and calculating the drop in each section, assuming the dimen- 
lioM civen by the approximate formulae. (See page 264.) If the pressure 
yop at the end of the line thus calculated diners considerably from the 
pcnmaable drop ^ven, chooee a lar^r sise wire and make another trial 
•ilealation, etc., until the proper sise is found. 




278 



CONDUCrOBS. 



u 



i. 



<— il — *- 



2 



-h 

Fio. 15. 



In the figure let G be the generating end of the line; / the far end off 



Given: 

B — pressure between adjacent wires at far end of line In volte. ' 
Wt, Wf, W9, etc., the loads in kilowatts at the points 1, 2, 3, etc. 
^1 ^ ^ eto^ the distanoes of these points from the generating end ia 

feet. 
P ■- per cent pressure drop at far end of line in terms off ddivend 

pressure. 
Required: 

A — cross section of each wire in million CM. 
to » total weight of conductors in pounds. 

Put ^ 

TT - TTi + TFa + TTs + . . . total power delivered in kilowatts. 
I " li + It + h + ' ' • total length of drowt (length of each wire) infeet 
kWi + hWt + ItWi + ... 



F - 



E^ 



Then, for a line havino no reactance: 



Cross section in million 
CM 

Total weight of conduc- 
tors 

Or total wei^t of con- 
ductors 

Vlar«« Plfta««. 

Cross section in million 
CM 

Total weight of conduc- 
tors 

Or total weii^t of oon- 
ductoxB 



A - 

w •» 

u> — 

A - 
w — 



Copper. 
100% conduc- 
tivity. 
20° Centigrade. 



2.08F 
6.06M 



12.6F{ 

~P 

1.041^ 

P 
0.09U 

0.48F2 



Aluminum. 
62% conduc- 
tivity. 
20**Centigrade. 



3.34F 
1.83U 



6.11FZ 

1.67F 

~ 
2.741A 

4.58F2 



Any MatenaL 
P"B meitihnis 

per eu. in. 
^■"Ibs.per 

ou. in. 



3.06pF 

P 

18.9<Li 



P 
1.53pF 

P 

28.3aLi 

4A.2pnF 



^ 



TRANSMISSION LINE CALCULATIONS. 279 



When the distanoes between the points at which the line is loaded are 
eooildetmble, it is ustially advantageous to taper the conductor; the most 



^ff^f^^m'"^^ pressure drop per section must be determined, and each section 
of the line calculated mdependently. The following formuke give the 
iDost eeooomical division oi the drop, taking into account the cost both 
o( conductor and insulation. For snort runs the saving in cost of con- 
ductor and insulation may be more than offset by the extra cost of handling 
tvo or more sizes of wire. 

The same notation as in the preceding paragraph Is used. In addition, 
let 

Vt^Wi-^- TTj + TTi 4" • • • "• total load in kilowatts at and beyond point 1 . 
(^ <- ITs 4- Wt +..."*> total load in kilowatts at and beyond point 2. 
Ob - YFs + ... as total load in kilowatts at and beyond point 3. 
eU. 



A| B 2| aa distance in feet from generating end to point 1. 

Af — 4 — 'i ■" distance in feet between points 1 and 2. 

^ " ib — b -■ distance in feet between points 2 and 3. 
e. 
Then the most economical per cent pressure drop for the tth section is 






Ai a mtei the sise of wire used in wiring ordinary bufldings for light 
•ad power as fixed by the permissible heating of the wire (see p. 265) is of 
niaeDt nse to keep the pressure drop within the prescribed limit, since 
the distances the wires are run are comparatively short. It is always well, 
bovcfsr, to calculate the drop in the heaviest and longest circuits, to be 
■OR that one is on the safe side as regards regulation. 

Cksrt wad Val»l« for CAlcelatfns' Altcntafing'-Cnrreat 

Baxph D. Mkbshon, in American Electrieian, 

Aeaeoompanying table, and chart on page 232 include everything neces- 
wy for ealcalatlxig the copper of alternating-current lines. 

Ihetehns, reslstanoe volts, reelstanoe E.M.F., reactance volts, and react- 
iKeEJI.F., refer to the voltages for overcoming the back £.M.F.'8 due to 
t«iit«Dce and reactance respectively. The following examples Illustrate 
Um use of the chart and table. 

FBOBLEJf.— Power to be delivered. 260 k.w.; E.M.F. to be delivered, 2000 
Tolti; distance of transmission, 10,000 ft.; size of wire, No. 0; distance be- 
tVMD vires, 18 inches ; power factor of load, .8 ; alternations, 7200 per min- 
ote. Knd the line loss and £rop. 

The power factor is that function by which the apparent power or volt-am- 
pereg most be multiplied to give the true power or watts. Therefore the 

qiPimt power to be delivered 18^^^ = 312.6 apparent k.w., or 312,600 

tolt«iiperei, or apparent watts. The current, therefore, at 2000 volts will be 

~j|ilip= 166.25 amperee. From the table of reactances, under the heading 

^ ISiBc hes,** and eorreBponding to No. wire, is obtained the constant. .228. 
Msriag the iMtmettooj of tM table in mind, the reaotanoe volts of thif 




280 OONDUCTOBS. 

line are 166.26 (ftrnperoB) x 10 (thousands of feet) x '228 = 366^ Tolto* 
are 17.8 per cent of the 9000 TOits to be deUvered. 

From the oolamn headed " Besistanee Volts," and oorrespondiiiff to Kaj 
wire, is obtained the constant .197. The reslstanoe Tolts of the line 
therefore, 166.25 (amperes) x 10 (thousands of feet) x .197=807.8 Tolta, ^ 
are 15.4 per cent of the 2000 Tolts to be delivered. 

Starting, in accordance with the instructions of the sheet, from the 

where the vertical line, which at the bottom of the sheet is marked **] 

Power Factor .8," intersects the inner or smallest circle, lay off horixoni 

and to the right the resistance E.M.F. in per oent (16.4), and " from 

point thus obtained," lay off. vertically the reactance E.M.F. in per 

(17.8). The last point falls at about 23 per cent, as given by the circmar « 

This, then, is the drop in per oent of the E.M.F. acliverea. The drop in 

28 
oent of the generator E.M.F. is, of course, , = 18.7 per oent. 

The resistance volts in this case being 3077, and the eurrent 166.25 
peres, the energy loss is 807.8 x 166.26=48.1 k.w. The percentage loss 

48 1 __ 

^iqI^i = 16.1 . Therefore, for the problem taken, the drop is 1S.7 per < 

and the enercy loss is 16.1 per cent. 

If the problem be to And the siae of wire for agiven drop, it must be sob 
by trial. Assume a sixe of wire, and calculate the drop in the manner aboi 
indicated ; the result in connection with the table will show the direct' 
and extent of the change necessary in the siae of wire to give the reqi 
drop. ' 

The table is made out for 7200 alternations per minute, but will answi 
for any other number. For instance, for 16,000 alternations, multiply 
reactances by 16000 -f 7200 = 2.22. 

As an illustration of the method of oalculating the drop in a line and 
former, and also of the use of the table and chart in oalculating low-roll 
mains, the following example is given :~ 

Pboblbm . — A single-phase, induction motor is to be supplied with 20 

Sres at 200 volts ; alternations, 7200 per minute ; power factor, .78. '. _ 
itance from transformer to motor is 160 ft., and the line is No. 5 wire,( 
inches between centres of conductors. The transformer reduces in the 
900O : 200, and has a capacity of 25 amperes at 200 volts ; when deliverii 
eurrent and voltage, its resistance £ JC .F. is as 2JS per oent, and its rea 
E.M.F. 6 per cent, both of these constants being furnished by the mak4 
Find the drop. 
The reactance of 1000 ft. of circuit, consisting of two No. 6 wirea, 6 ini 

IfiO 

I4>art, is .204. The reactance-volts, therefore, are .204 x jg^ X 20= .61 Tolta. 

The resistance-volts are .627 x j^ X 20 = 1.88 volts. At 26 amperes, the re> 

tlstanoe-volts of the transformers are 2Z per cent of 200, or 6 volts. At 90 

amperes they are ^ of this, or 4 volts. Similarly, the transformer reactance 

volts at 26 amperes are 10, and at 20 amperes are 8 volts. The combined re- 
actance-volts of transformer and line are 8+ .61 = 8.61, which is 4.3 per cent 
of the 200 volts to be delivered. The combined resistance-volts are 1.88+4, 
or 6.88, which is 2.94 per cent of the E.M J. to be delivered. Combining these 
quantities on the chart with a power factor of .78, the drop is 6 per cent of 

the delivered E.M.F., or t^ = 4.8 per cent of the impressed E Ji.F. The 

transformer must therefore beaupplied with 2000 -r .962 = 2100 volts, in order 
that 200 volts shall be delivered to the motor. 

To calculate a four-wire, two-phased transmission eirouit, oomputo, aa 
above, the single-phased circuit required to transmit one-half the power at 
the same voltage. The two-phase transmission will require two such 
eireuits. 

To calculate a three-phase transmission, compute, as above, a single-phaae 
eirouit to carry one^half the load at the same voltage. The three-phswe 
transmission will require three wires of the slse obtained for the sliigia-phaae 
circuit, and with the same distanoe (triangular) between centres. 

By means of the table calculate the Re*i$tanee- VoU$ and the 



1 

TRAN3MtaSION UNE CALCULATIONS. 281 



i 
i 



» 



CONDUCTORS, 



TBANSMIBSIOH LINE C 

wine suma publiihed by the 0«aeral E]«tric Compuiy (ira 
al «>pp«T per kitowatt (Mivmd for varioua paroeatace* of powv 
ioiB preaaun indieDU (volla per mile). It i* lo be Dat«d thM 
I are eorrecC only for unity poim [actor. 

liui Leas in par cent of Pomr Delivered- 



i 

i 

{ 



rrealndlcateTOltapernilte, I.e., potential 
iRlit of eoppar, potBiiHa!, sad Udb Iobb ws 

CarTca are «oiTeet onW (ot 100% power factor. Tirn-piiiih«, Biiigle-pbflM 
or CODtlanaiu eurrenl iiuumlsaion requires one-third more cupper. E% 
Ui beni allowed for eag and tie virea In welahta of copper given. 

ExAMPUt Aaaamlng that 1000 k«, at lOloOO volte are to tie dellTered 
ortt a Uue 10 mllea lon( irltb S% loH, wo bavo -"fl"^!!^'- - "W Tolti 
per mile. Looking on tbe ICOO TOlt curve, we flna G% line loee oorreapondl 
la SI lU. of copper per kilowatt delivered. 



284 CONDUCTORS. 



DDXBiunEHrAxioir or bwmm oc comtircvoits rom 
PAiftAULJBii DiATimuanioir or doibct 

Beaifltanoe of one oir.-mll-foot Of pure hard drawn copper wire 

at aO» C. (68° F.) (see page 200) lO^ohiiit 

Resifltance uz one cir. -mil-foot of pure hard drawn oopper wire 

at 97JS per cent oondttctirity 10.6 obiot 

Thus the resistance R of any hard drawn copper conductor is, 




and 



or 



^ length i n feet X 10.8 
cir. mils ' 

Clr. mil. - '^i^ *" '«*' ^ "•* 



Length in feet 



Ji 

R X cir. mils 
10.8 



Let / — Current in amperes flowing in circuit. 

^ . Watts, power in circuit. 

E « Volts at reoelying end of circuit. 

V — Volts drop in circuit. 

A <" Cir. mils area of wire. 

P •- Per cent of power lost. 

p >■ Per cent of volts drop in circuit. 

d — Distance from generating to receiylng end of circuit or center 
of load»^ the length of wire if the load is uniformly dlA* 



tributed. 
21.6-10.8X2. 



Then 



or 



or 



. 21.6 X dX / 
^ - ^ . 

. 2160 X J X / 
^ PX~B • 

2160 X dxjr 

^ 21.6 Xd XI 
V -^ . 

100 



T&AK8P08ITI0N OF LUfXS. 



■mAirspoaxnoH or iMMxm. 

F. F. Fowi^ 

of OTarhflad linn ii ft nwana for eliminatiiis in 
uniwBaUy aroployttl on tcLopbone linM aod Qi 



only und( 



Lnd th« muTHtJo fields about & lins econAtlD^ of a luulo 
ia eomplaMd thcoucli the Muth. Fif . Ja ibon tlu Gald* 



Fig. 18. Fio. 10. 

>boM 111* two wira <4 a malallio alrouil. will) «tual and oppoaiM curmila 
in Iba vim and no ceriDsclioii U> aatth at any poinl oa the oiniuit. lo 
M^booT this CDndition ri lins is termad " baUncnd." 
tat iotendty of ths inducsd eumnt dspends on thg aileot to which th« 

; Md <rf ana eirouit thnadi into the othsr. and tbonfore upon the diitanoe 
tMnea the wires and the eitent to which Ibsir fields spnad bio the sur- 
nmdiiif dieleetrie. The ipnod ot the Geld of a linila-wire circuit, shown 
n Rf. IS. is equsl to that ol an imuinBry mstaliiB circuit c^ which one 

I vm m the sidsejng overiiead wli« and the other a ■'"*"*r wire puaUd to 

c I 



i 

i 



1 «> 






1* 



Fro. 2a 

Um nistins wlra but beneath the eanh's surfaos a distance equaJ to tha 
•JevmOoB rf the eiiitiTis wire. The tpr«Kl of the field of .initle-irire eartii- 
"ratD cireuits is therefore eioenive. 

fif. 20 shows the maoner of neutralisinB mutual inductive effects of 
Iw DMalGe rircnits by the tianspojition ofthe wires nf one circuit. By 
UK Inaqxisitian of Rircn 3 and 4 midway in the section the licld nf the 
BTtrnt M from a lo fc is oppomle in it4i direction and polarity to that be- 
l<nai b and e. so tliat the induced E.M.F.'i in circuit 1-^2 between a and b 
*" oppoate to thoM between b and c The same is true of induced E Jd.F.'a 



286 



CONDUCTORS. 



V ^^u^} ?^ prod***^ ^y mrouit 1-2. Tha effecta would have been idea- 
ti<^I had 1 and 2 been transpoeed instead of 8 and 4. 

Kefemng to Fig. 20, the Itm^th of the section I must not be so sreat tha 
the current and the potential in the section (t-b are materially diffmnt fnm 






X 



X 



-f- 



-4^ 



D 



•«- 



t 



3!) 



Fia. 21. 



WnSi^^'^^^^ i^cL^^^tj^SeTXSsSrbT^^^r 5 ^ 

Se^tinS^Vnf'i?^' '^* ™^«. ^.^*»« measurem^Irof a^disSSSe « 
iJliS^l;?***^ **^ **°if " ^°* * multiple of Z. the last section may be Uken 
somewhat longer or shorter than the stand»^ section, but it shduW bs S 




Fio. 22. 




Fig. 22A. 

more than one and a half regular sections nor less than half a regular see* 

tion. Fig. 21 shows a line haying four and a quarter transpositio?seotiSL 

A transposition at the junction of two adjacent sections is wi^iTnnt *^M«t 

on those sections, therefore the Fig. 22A ii ^uivSeLTto F^S-^^ fwl 



A 



^ 4^ 



3 



Fio. 23. 



TBABTSPOSITION OF LINES. 



287 



^ 



b tins only when the standard section length is not in excess of that per- 
misrible, as outlined above. 

The transposition of power and lighting drouits is not often necessary. 
In Qomplicated networlu it is almost unKnown, because the troublesome 



C 



n 



^ ^ ^, 



w 



Fig. 24. 



oreoits are asoally short. At the frequencies used in power and lighting 
the. transposition section may be several miles in length, much longer than 
in tdephone practice. 

The transpctfition of polyphase lines is sometimes employed to balance 
ndafitive effects which would otherwise be troublesome. 




!; 



5^ 



K 



V—w-' 



■H4- 



-^ 4 



■2 



■;3 

I 



Fio. 25. 



F%. 23 shows a balanced three-phase line, which would be transposed 
QOly to avoid inductive interference with other lines. 

Fig. 24 shows an unbalanced three-phase line and Fig. 25 shows the 
BvUiod of transposing it to secure a balanced circuit, or eaual inductance 
per phase. Fig. 28 illustrates the application of the section shown in Fig. 8. 



I 




1— 



4 1 - 

Fia.26. 



3E 



Tlis transposition of telephone lines becomes a complicated problem when 
tfane are many circuits, as it is necessary to arrange the transpositions in 
nidi s manner that each circuit is transposed with respect to all the others; 



r 



288 



GONDUCTOB8. 



Also the drouita that are adjacent must have more frequent relative iraae* 
poeitiona than those further apart. The method of deriving differently 
transposed types of circuits is given in an American Institute paper on 
"The Transposition of Electrical Conductors." * 

Fig. 27 shows fifteen different types of transposition. The "expoeure," 
as it is termed, of circuit 1 to circuit 2 is i; of 1 to 3 is i; of 2 to 3 is i; 
because a transposition at the junction of two sections, ea<ui tran^poeed at 



1^ 



Komberof 
Traiufposltioitt 



0- 

i: 



81 



e: 
t: 
&: 



9: 

ID' 
XL 



DC 



3C 



X 



(^ 



I- 



XZXIX 



XZXZDC 



X 



3CZ3CDC 



i^^^H^^^^^H^^^M 



DCZDCDC 



y — x—r 



Tjpe BerlTatici 
No. ofTn» 

no 



:8 - n- « 



1^5 -1+4 
ZZI6- «-^4 

=17 -8 + 4 

Dczrs 

xz:9 » 1 + 8 

DCZ:10"8 + 8 



■^■^■■^^■^i^^^ 



X.X X. 



^^^^a^^^^mm^^m 



xzxzx 



Dczxzx: 



^^H^H^klV^/^M^B^«^B^\^^B^\^l^^^^ 



DCDCDC 



XZIU- 8 + 8 
:i8a4 + 8 
lis- 6+8 



18 

11— y V Y-v—v— > r-y y — v— r-Y-^x— Y-n< 14»ii -i- 8 

151 „ )R X y . x X tLJH ■ j i . rn t X X-IXI-X— x m * 7 + 8 



i^^ 



^ 



DCZ318-7 



Fia.37. 



ita eenter. has almost no beneficial effect. The exposure of 1 to 5 is f; of 
2 to 6 and 3 to 7, ^; of 2 to 8 and 2 to 9. A ; and so on. The tabulated ex- 
postves are given m Fig. 28, in terms of the length 1 of a transposition 



tion. The method may be extended as far as desired, but 15 types ars 
usually sufficient. 

It has been found' experimentally that one-fourth mile exposures are sat- 
isfactory in telephone work for circuits immediately adjacent to each other; 
for circuits not adjacent the transpositions mav be farther apart. The 
distance I in Fig. 27 may then be taken at four miles, and fifteen differently 
transposed types are available. The method may be extended to thirty- 
two types with an eight mile section. The eight mile section is rather 
cumbersome for most work and a four mile section is more adaptable to gen* 
eral conditions. 

The transposition of telephone circuits a^inst power and lighting circniti 
should be treated on the sectional principle. It is possible to improve 
some cases by reducing the separation between the wires of the power or 
lighting circuit; this is usually the cheapest plan if the transposition section 



• Vol. XXIII. page 659, Oct. 28, 1904. 



■TBAMBPOSITIOH OV LINB8. 



fiOOoTia duuibui 

A^ poiQl* when telephoiie Ud< 



Uiapbooa dreuit*. For the toIU^v* len thui 






Expoaiin otTyiM No. 



To 





1 


. 


. 


. 


• 


. 




a 


, 


10 


11 


i: 


13 


,4 


1 


- 


















i 


















i 


















4 






























! 




i 


t 


i 


) 




- 


















« 




* 


i 


1 


i 


1 


















7 


i 


* 


t 


t 


I 


i 


1 


















B 


i. 


A 


A 


A 


A 


A 


A 


A 
















. 


A 


A 


A 


A 


A 


A 


A 


A 
















10 


1, 


A 


A 


A 


A 


A 


A 


A 
















11 


A 


A 


A 


A 


A 


A 


A 


A 
















IJ 


A 


A 


A 


A 


A 


A 


A 


A 








» 








13 


A 


A 


A 


A 


A 


A 


A 


A 








* 


i 






14 


A 


A 


A 


A 


A 


A 


A 


A 








* 


i 


t 




IS 


A 


A 


A 


A 


A 


A 


A 


A 








1 


1 


i 


i 



i 



m two mdiictjc 






Tha procedure ie to hr 



• in the dinr 
on will Dot b 



jutinc circaiU, u on oppoaite ndea of theee 

nee are ncpoMd to oompU»ted dietributk 
lie, it DO( effeetiTe. 




290 



GOKDUCTOB8. 



B 



s 



1 



1 



ladoctton 



8«otioa 



•*• 



Indpotton 



I r. 



Indaetton 



Sootion 



Inductio n 



Fto. 20. 



Mfavara lif ■•• — The condaeton on this line are bare eables of II 
Btrands, equlTalent to 360,000 circuit mils, and are arranged aa shown in 
the fonowing diagram. The first arrangement was with two three-wire eir- 




FlO. dO. Niagara-Buffalo Line. 11000 to 22000 VolU. 

onlts on the upper cross-arm, the wires being 18 inches apart. Bo mueh 
trouble was experienced from short ctrenits by wires and other material 
beins; thrown across the conductors, that the middle wire was lowered to 
the bottom cross-arm as shown, 'since which time no trouble has been 
experienced. With iK>roelain insulators tested to 40,000 volts there is no 
Appreciable lealcaffe. These circuits are Interchanged at a numbs* of 
points to avoid inductive effects. 



TRAirSPOaiTIOIT OF LINKS. 



291 



Ctvcoite* — « The diagram (Fig. 81) shows another ar- 
xangement now eeldom used although it nuikes lines oonyeniently aooeesible 
for rqpaira. Under the ordinary loads usual in the smaller plants the unbal- 
andiig ^ect is so small as to be inappreciable. . 





Fio. 31. Convenient Arrangement of Three-Phase Lines fori 

6000-10,000 Volts. 






.X. •&! 



• a. 




I 



Fio. 32. Arrangement of Two-Phase Circuit. No Reversal 

of Phases necessary. 



( 



Tw«.|Phae«, Conr-is'lre Clrculte. — The arrangement of conductors 
•nown in Fig. 32 is probably the best for two-phase work; as no reversals 
cK wires are needed, the inductive effects of the wires of one circuit on those 
« the other are neutralised. 



292 CONDUCTORS. 



Vwo-Pluw« Ctvcoltw te Wame P1»b«i. — If the phases are traal 
u separate cireuits, and earned well apart, as shown in Fig. 33, the inl 




PHASE B. 
18^^ Ht 18^ 



Fio. 33. 

enoe is triflins; and should the loads carried be heavy enough to cause notioe* 
able effect, the reversal of one of the phases in the middle of its length will 
obviate it. The following diagram illustrates the meaning. 



PHA8E A. 
1 



PBA8 E B. > (^ 



Fio. 34. Arrangement of Two-Phase, Four-Wire Circuit with Wires on 
same Plane. ^Wires of One Phase should be interchanged at the Middle 
Point of the Distance between Branches, and between its Origin and 
First Branch. 

Messrs. Scott and Mershon of the Westinghouse Electric and Manufactur- 
ing Co. have made special studies of the question of mutual induction of 
circuits, both in theory and practice; and their papers can be found in the 
files of the technical journals, and supply full detau information. 

Mataal Hevtrallaattoii of CapACtly aad ladvcteace. — In 
order to completely neutralise j^hase displacement due to distributed in- 
ductance a distributed capacity is essential. Localised cai>acity can, how- 
ever, produce a partial neutralisation. Ehceessive distributed cafiacity 
can also be partially neutralised by inserting inductances at proper inters 
vals. In treating of local neutralisation of capacity by inductance, the 
assumption is frequently made that the capacity is constant irrespective 
of the voltage, and that the inductance is constant irrespective of the 
current. Under these conditions neutralisation can be obtained. As, 
however, inductance is dependent upon the permeability of the assodated 
magnetic cirouii, and permeability varies witn the saturation of the iron. — 
that is, with the current, — * complete neutralisation cannot be obtained 
with iron inductances. 

Over-«xcited sjaichronous motors, or sjrnchronous converters, take cur- 
rents which lead the electromotive force impressed upon them, and they 
therefore o|>erate as condensers, and they may be utilized advantageomly 
in neutralising the line inductance. The power factor of the transmisaion 
ssrstem can therefore be varied by varying their excitation. 



BELL WIRING. 



293 



COVBJUBl^ GAJBUM. 

Jobs T. Uorsib {Slectridant London) gjves the following formula, con- 
finned by experini«ntfl, for the loas of power in the lead sheath of a three- 
Amdoelor cable. 
Let J « current in amperes. 

/ — frequency. 
I — length of cable in 1000 ft. 

£ » thic 

Thco: 



t » thickness of sheath in mils. 
Watts lofls - 123 X lO'^Pf^lfi-^ 



If the eaUe is placed in^ an iron pipe the loss is increased about 75%. 



]s;bia iraurare. 

The following diagrams show various methods of connecting up-call bells 
for different purposes, and will indicate ways in which incanaescent lamps 
Bsy sho be eonnected to accomplish different results. 



=4 



Q=W 




fim. 35. One BeO, qpemted by 
One Push. 



Fia. 96. One Bell, operated by 
Two Pushes. 






G 



i 




P>B. 37. Two Bells, operated by 
One Push. 



Fio. 38. Two Bells, operated by 
Two Pushes. 



When two or more bells are required to ring from one push, the common 
pnetice is to connect them in series, i.e., wire from one directly to the next, 
snd to make all but one single-stroke ends. Bells connected in multiple 
•re, M in diagram Ho. M, glye better satisfaction, although requiring more 

vixe. 



i.i-fi— ! 



^•9. Three-Line PMtory Call. 
A amber of Bells operated by 
ttynmnber of pushes. All bells 
niog by each push. 



£ 




FiQ. 40. Simple Button, Three- 
Line Return Call. One set of 
battery. 



F 



SCMM 

Tm> 41. Blsr^e Button, Two>Llne 
tDdOrofmdB«tvimCaU. One set 
of battery. 



& 



3*] 



Fio. 42. Two-Line Return Call. 
Illustrating use of Return Call 
Button. Bells ring separately. 



294 



CONDUCTOBS. 



^ 



t 



& 



ii!i 



Fia. 43. One-Line and Ground Betum 
Call. lUuBtrating use of Return Call 
Button. Bella ring separately. 



Fig 4i. Simple Button, Tv< 
Line Return Call. Bella 
together. 




i 




i 




Ftg. 46. Simple Button, One-Line 
and Ground Return Call. Bells 
ring together. The use of com- 
plete metallic circuit in place of 
ground connection is adylsed in 
all cases where expense of wire 
is not considerable. 



Fig. 46b Four Indication Annunoia- 
tor. Connections drawn for tv 
buttons only. A burglar alarm dr* 
cult is similar to the above, bul 
with one extra wire running frmii 
door or window-spring side of bat- 
tery to burglar alarm in order to 
operate continuous ringing attach* 
ment. 



C^ 






Fig. 47. 

m of connections for control of lights from two points. 



) 




qhsslJ^ 



Fig. 48. 

Dia^pttm of connections for control of lights from four points. By in- 
troducmg other switches like A and B control can be had from any number 
of points. 



d 



M. 






^nssassk 



Fig. 40. Four Indication Annuncia- 
tor, with extra Bell to ring from one 
Push only. Illustratii^ use of 
threo-point button. 



|f\ j^ 



Fig. 50. Acoustic Telephone with 
Maf^neto Bell Return Oall. Ex- 
tension Bell at one end of fine. 



TRANSTOBMERS. 



295 



In nnmins lines between any two points, use care to plaoe the battery, if 
. iwbkL near the push-button end of the line, as a slight leakage in Uie dr- 
enit win not then weaken the battery. 



When mat is to be used, throw it into the oircuit 
by the twitch, so that when the circuit is closed by a 
penon stepping on the mat, the automatic drop will 
keep it dosed, and both bells will oontinue to ring 
mul the drop is hooked up again. 



Fig. 51. Diagram of Burglar-Alarm Mat, two Bells, 
Qoe Poeh and Automatic Drop; all operated by one 
bstterv. Both bells ring from one push or mat, as 
dewed, by changing Uie switch. 






Fie. 53. Pendant and Automatic Gas- Fio. 63. Pendant Qas-Iighting Cir- 
U^ting Circuit, with Switchboard. cuit, with Switchboard, Relay 

and Tdl-Tale BelL 



The generators are rated by their volt-ampere capadty and thdr appai 
vatu, and not their actual watts, so that the mse has to be increased if 
poTO-fsetor of the system is low. 



rent 
if the 



I 



WJ[KKli« V^U TltJLlVSFOMMBmS. 



For lighting eirrndts using small transformers, the voltage at the prima- 
nyo l the step-down transformers should be made about 3% higher than the 
t^taodagf voltage multiplied by the ratio of transformation, to allow for the 
drop in tiansformers. ui large lighting transformers this drop may be as low 
M 2%. Standard lighting transformers have a ratio of 10 to 1 or some m\il- 
tiple thereof . 

For motor drcwts, the voltage at the primaries of step-down transformers 
uoold be made about 6% hithte than the secondary voltage multiplied by 
we nUo of transformation. Transform<»« used with 1 10 volt motors on any 
f^ vnrimn should have a ratio of 4i to 1, 9 to 1, or 18 to 1 respectively 
^ 1040, 2060t and 3120 volt generators. The transformer capacity in kilo- 
*s8t ihoQld be the same as the motor rating in hone'pawer for medium-sised 
potori, sad slis^tly larger for small motors and where only two trans- 
"nners are used. 



296 



CONDUCTOaS. 



0»pttcitte« of T 



fomi«ni to b« 
Iiftdactlon Motoni. 



wttM 





Kilowatts per TraoBformer. 


Size of Motor. 




Hone-Power. 








Two Transformers. 


Three Transformers. 


1 


.6 


.6 


2 


1.5 


1 


8 


2 


1.5 


5 


3 


2 


7i 


4 


3 


10 


5 


4 


15 


7.5 


5 


20 


10 


7.5 


30 


15 


10 


50 


25 


15 


75 




25 



friJEuor« FOR inmjcnoiv hkoxora. 

The standard (General Electric) induction motors for three-phase cir- 
cuits are wound for 110 volts, 220 volts, and 550 volts; motors of 50 H.P. 
and above are, in addition, wound for 1040 volts and 2080 volts. Motors 
for the two latter voltages are not built in sizes of less than 50 H.P. Where 
the four-wire, three-phase distribution ssrstem is used, motors can also be 
wound for 200 volts. 

The output of an induction motor varies with the square of the voltas» at 
the motor terminals. Thus, if the volts at the terminals happen to be 15% 
low, that is, only^ 85% of the rated voltage, a motor, which at the rated volt- 
ace gives a maximum of 150% of its rated output, will be able to give at the 
l5% lower voltage, only (^)^X 150— 108% of its rated output, and at full 
loaia will have no margin left to carry over sudden fluctuations of load while 
nmning. 

Thus it is of the uftmoBt importance to take care that the volts at the motor 
terminals are not below the rated volts, but rather slightly above at no load, 
so as not to drop below rated voltage at full-load or over-load. 

The output of the motor may be increased by raising the potential; in 
this case, however, the current taken is increasecf, especially at light loads. 
The direction of rotation of an induction motor on a three-phase circuit 
can be reversed by changing any two of the leads to the field. 

Like all electrical apparatus, the induction motor works most efficiently 
at or near full load, ona its efficiency decreases at light load. Besides this, 
when nmning at light load, or no load, the induction motor draws from the 
lines a current of about 30% to 36% of the full-load current. This current 
does not represent ener<:;y, and is not therefore measured by the recording 
watt-meter; it constitutes no waste of power, being merely what is called an 
idle or ''wattless" current. If, however, many induction motors are oper* 
ated at light loads from a generator, the combined wattless currents of the 
motors may represent a considerable part of the rated current of the gene- 
rator, and thus the generator will send a considerable current over the line. 
This current is wattlecs, and does not do any work, so that in an extreme 
case an alternator may run at apparently half-load or nearlv fulMoad cur- 
rent, and still the engine driving it nm light. While these idle currents are 
in general not objectionable, since they do not represent any waste of 
power, they are undesirable when excessive, by increasing the current-heat- 
ing of the generator. Therefore it is desirable to keep tlie idle currents in 
the BysienL as low as possible, by carefully choosing proper capacities of 
motors. These idle currents are a comparatively small per eent ol the total 



CONNECTIONS. 



29T 



■^ 



eorrent at or near fall-load of the motor, but a larger per cent at light loads. 
Therefore care should be taken not to install larger motors than neoessarv 
to do the required work, since in this case the motors would have to work 
eontinuoualy at light loads, thereby producing a larger per cent of idle cur- 
rent in the system than would be produced by motors of proper capacity; 
that is, motors running mostly between half-load and full-load. 



C«rraat taken l»j 



C^nenil Electric Co., Tli: 
■ Metors lat UO l^olta. 







Starting 


Starting 


H.P. of Motor. 


Full-Load 


Current at 


Current 


Current. 


150% of FuU- 
Load Torque. 


at Full-Load 






Torque. 


1 


6.5 


10 




2 


12 


36 




3 


17 


54 




5 


28 


•42-84 


28 


10 


55 


70 


55 


15 


80 


120 


80 


20 


105 


167 


105 


30 


150 


252 


150 


£0 


250 


400 


250 


75 


370 


585 


370 


100 


600 


825 


500 


150 


740 


1180 


740 



l^e current taken by motors of higher voltage than 110 will be proportion- 
ally leas. The above are average current values, and in particular cases the 
▼klosB may vary slightly. 



comrsenoiTA oi* oniAirsvoiuiisiis x-os irisiirc}. 

The connection of three transformers, with their primaries, to the genera- 
tor and their secondaries to the induction motor, m a three-phase system, 
are ghovn in Fig. 26. The three transformers are connected with their pri- 
mvies between the three lines leading from the generator, and the three 
Keondaries are connected to the three lines leading to the motor, in what 
ii called delta connection. 

Tht connection of two transformers for the supply of an induction motor 
(nnn a three-pliase generator is shown in Fig. 56. It is identical with the 




^F 



ToTOt 



Fio. 64. 



FlO. 65. 



vnngement in Fig. 64, except that one of the transformers is left out, and 
ttietTiro other transformers are made correspondingly larger. The copper 
f^qidred in any three- wire, three-phase circuit for a given power and loss is 
^« u compared with the two-wire, single-phase, or four-wire, two-phase 
^tem, haying the same voltage between lines. 



* The 5 H.P. motor is made with or without starting^witch. 



298 



CONDUCTORS. 



The connections of three transformers for a low-tension distribution ays* 
tern by the foar-wire, three-phase system are shown in Fig. 56. .The thras 
transformers have their primariesjoined in delta connection, and their mo- 
ondaries in '* Y " connection. The three upper lines are the three main 
three-phase lines, and the lowest line Is the common neutral . The differenee 
of potential between the main conductor is 200 volts, while that between 
either of them and the neutral is 115 volts. 200 volt-motors are joined to the 




I 



^31 



~3i: 



s 
I 



Fio. 66. 



Fio. 67. 



mains while 116 volt-lamps are connected between the mains and the neutraL 
The neutral is similar to the neutral wire in the Edison three-wire system, 
and only carries current when the lamp load is unbalanced. 

The potential between the main conductors should be used in the formulB, 
and the section of neutral wire should be made in the proportion to each of 
the main conductors that the lighting load is to the total load. When lights 
only are used, the neutral shomd be of the same size as either of the wree 
main conductors. The copper then required in a four-wire, three-phase sys- 
tem of secondary distribution to transmit a given power at a given loss is 
about 33.3 %, as compared with a two-wire, single-phase system, or a fonr- 
wire, two-phase system having the same voitage across the lamps. 

The connections of two transformers for supplying motors on the four-wire, 
two-phase system are shown in Fig. 57. This system practically consists of 
two separate single-phase circuits, half the power being transmitted over 
each circuit when the load is balanced. The copper required, as compared 
with the three-phase system to transmit given power with given loss at the 
same voltage between linesi is 133i % — that is, the same as with a single- 
phase system. 




STANDARD BYMBOLS FOR WIRING PLANS 

AS ADOPTED BY THE NATIONAL ELHO- 

TRICAL CONTRACTORS ASSOCIATION. 

(Copyrighted.) 

S{ Celllns Outlet; Electric only. Numeral in center iadioatai 
number of Standnrd 16 G.P. Incandescent Lamps. 

K^ Celling Outlet; Combination. | indicates i-16 C.P. Standard 

Incandescent Lamps and 2 Oas Burners. If gas only ji( 

Bracket Outlet ; Electric only. Numeral in center Indieates 
number of Standard 16 C.P. incandescent Lamps. 

Bracket Outlet ; Combinations. | Indicates 4-16 C.P. Standard 

Incandescent Lamps and 2 Qas Burners. If gas only ^^^0i 

Wall or Baseboard Beceptacle Outlet. Numeral in center indi- 
eates number of Standard 16 C.P. Incandescent Lamps. 

^ Floor Outlet. Numeral in center indicates number of Standard 
16 C.P. Incandescent Lamps. 

i3 S Outlet for Outdoor Standard or Pedestal: Electric only. Numeral 
indicates number of Standard 16 CJP. Incandescent Lamps. 

tt-f- Outlet for Outdoor Standard or Pedestal ; Combination, t iudi- 
** cates 6-16 C.P. Standard Incandescent Lamps ; 6 Qas Burners. 




Drop Cord Outlet. 

^ One Light Outlet, for Lamp Beo^tacle. 

d Arc Lamp Outlet. 

ft Special Outlet, for Lighting, Heating and Power Current, as 
described in Speciileations. 

^^OO Ceiling Fan Outlet. 

S^ S. P. Switch Outlet. 

S* D. P. Switch Outlet. 

S^ 3-Way Switch Outlet. 

S* 4-Way Switch Outlet. 

3° Automatic Door Switch Outlet. 

3^ Electrolier Switch Outlet. 

B M«ter Outlet. 
^^ Distribution Panel. 
^1 Junction or Pull Box. 

J^ Motor Outlet ; Numeral in center indicates Horse Power. 

Motor Control Outlet. 

Transformer. 

209 



Show as many Symbols as there 
are Switches. Or in case of a 
very large group of Switches, 
indicate number of Switches 
by a Roman numeral, thus ; 
S^XII; meaning 12 Single Pole 
Switches. 

Describe Type of Switch tn 
Specifications, that is, Flush 
or Surface, Push Button or 
Snap. 



< 



300 



STANDARD SYMBOLS FOR WIRING PLAKS. 

Main or Feeder run concealed 
under floor. 



Main or Feeder run concealed 
under floor above. 

""■■■■ Main or Feeder run exposed. 



Branch Circuit run concealed 
under floor. 

Branch Circuit run concealed 
under floor above. 



Heights of Center of Wall 
Outlets (unless otherwise < 
specifled): 

Livinff Rooms 6 ft. 6 ins. 

Chambers 5 ft. ins 

Offices 6 ft. ins. 

Corridors 6 ft. 3 ins. 



Heights of Switches (nnl^ 
otherwise specdfied) : 

4 ft. ias. * 



""""*■" Branch Circuit run exposed. 

•• — •• Pole Line. ' — 

• Riser. 
P Telephone Outlet ; Private Service. 

J^ Telephone Outlet ; Public Service. 
□ Bell Outlet. 

O^ Buzzer Outlet. 

S2 Push Button Outlet ; Numeral indicates number of Poshes. 
"N^ Annunciator ; Numeral indicates number of Points. 
-^ Speaking Tube. 

— © Watchman Clock Outlet. 

— 1 Watchman Station Outlet. 

— O Master Time Clock Outlet. 

— HD Secondary Time Clock Outlet. 

f7l Door Opener. 

B Special Outlet ; for Signal Systems, as described in SpeolfloaUons. 

l|l|l||||| I Battery Outlet. 

{Circuit for Clock. Telephone, Bell or other Service, run under 
floor, concealed. 
Kind of Service wanted ascertained by Symbol to which line 
connects. 

(Circuit for Clock, Telephone, Bell or other Servloe. run under 
floor above, concealed. 
Kind of Service wanted ascertained by Symbol to which line 
connects. 



UNDBBGBOUND GONDUITa AND 
CONSTRUCTION. 



Wrb tte Mtablishment of ihs fink eomnMroul Hone teltmph lint 
9R»bibly oommcnoM the hiatorv of Um "underground wire" when a. 
lokto-fiereha coTered eable wm laid in m tnsoh inade oy an oz-draim plough. 

8tavM in the evohition of the preeent "monolithio" conduit are promi- 
HBlly marked by the eyttem of croupinc wiiet permanently inetalled and 
■eperiled by the pourixue about them in the trenoh of vanoue inwikting 
•oa^oaads; by the " buut up ssrttem" made of oraoeoted boards ao plaeed 
at to form aqnare <^i*«»w*>i« or dueta; by the **pump log'' ayatem or aquared 
timber bored to required aiae and creoaoted; by the oament lined iron pipe 
CjaUm; by the uae of imper moulded and treated with dielectric oompounoa; 
lad hv the now -very huiely uaad Titrified elay. Olay oonduita ahouki be 
manaiaotured from a clay which will vitrify to a hishly homogeneoua and 
■oa-afaaoibfait condition and be free ficom chemical elamenta (iron, aulphur, 
atCL) wliifili under the action of heat in the kilna reault in nodea or buaten 
ia the ware. 

There are two eatabliahed atylea of olay conduit commonly deaignated aa 
"ncia duet" and "multiple duct." The atandard unit of the einale duet 
ii of aquaie eroea aection meaennniB 4^' by 4}" with oomen ohanueredt ia 
18 inebea in len^pth, and hae a 3| moh round core or hole. The atandard 
■aWple duet umte an of two, three, four, or aiz duct aectiona, the bore of 
each duct of any aection bein|; aquare and meaauilinj 3i bv 3}, the interior 
and exterior wall being f " thick; the lengtha of unite are, for two and three 
duet. M incfaea. and for four or aix duet 86 inobea. The demand for 3i inch 
aad 4 inch boree or even larger ia oonatantly increaaing. Multiple duct 
eooduit of nine duct and twelve. duct aecticma have been offered to the 
Inde but ao far have not come into extenaive uae. 

Siagle duct eonduita being mora flexible are better adapted to uae whera 
MTriee pipee, eurvea, or ofaetaelaa ara frequently encountered. Laid with 
bvofcea jomta the poaaibility of the heat from a burning cable, being oomf 
■mirateH to a neighboring cable, ia precluded. Where hi^ conatruotion 
OB a email baae (two dueta wide by more than five ducta high) ia required, 
•mdea ara not used to advantage. A maaon ehould, under fair working 
eoadttiona, average in a day of eiight houn from twelve hundred to aixteen 
handred duet feet of aingle duet conduit. 

Muhiplca have in thair frivor fewer joiata, ai eater weight per unit, and the a 

JMt tbat their installation requirea only unaJdUed labor. Two men aelected M 

mm a gang of laborera will lay from eighteen hundred to twenty-four hun- ■ 

dred duet leet per day of ten boura. 1 

Tkroo^ town or city atreeta the conduit ehould have a foundation of 
•PBcreie at leaat 3 indiea thick. Whera fre9uent excavationa for other 
eorke are probable a complete encaaement of 3 mchea to 4 inchee of concrete 
•honld be placed on both eidee and on top of the ducta. The aide protec- 
tion is, however, aometimea omitted and creoaoted boarda aubatituted for 
amerete on top. The top covering over ducta ehould be not leee than 24 
iaehea below the aurface of the atreet. 

Tk» aaverml comdmlt torme ara generally defined aa followa: 

The word "Conduit" meana the Mgregation of a number of hollow 
tebee of duet material and indudee aUof the ducta in a croee eeetion of 
Ike eubway. In general a conduit will conaiat of four ducta or mora. 

The woid "Duet" meana a aingle continuoua paaaageway between man* 
Bolee or through any portion of the conduit or laterals. 

The word 'llanhole" meana an underground chamber built to raeeive 
ilactrioal equipment and auitable to give acoeea to the conduit. 

The word 'Service Box" meana an underground chamber eimilar to a 
■aahoU but of emaller aiae, and deaigned primarily to give acceae to dia- 
triboting eondttctora. 

801 



302 



UNDERGROUND CONDUITS. 



Hm word "Lateral" meant one or more dueta extending from a maahole 
or eerrice box or from one or more of the main conduit oucte to aome dii- 
tributing point. In general Jaterala will oonsist of one or two ducts few the 
■ame service connections. One or more laterab may be installed in the 
same trench. . 

Manholes Vary >o much according to the ideas of the diffennt ensineera 
that it is' difficGUt to give data that would suit all of them. However, the 
average sise of manhole is 5' X 6' X 6' in the clear with a 12f waU. The 
covers for same vary from 800 to 1400 lbs. The general practice is to 
have vmtilated covers and sewer connections with automatic badc-watsr 
trans. 

The Servioe Boxes are made generally of concrete with an 8' wail, either 
S' X 2^ or 2' X 3' in len^^h and width, and extending in most eases to the 
top \tkyet of the conduit system, which would make the depth of tfas 
servioe boxes vary according to the depth of the conduit system proper, 
the upj;>er tier of duets being used for distribution. Covers for servioe bo3 
inchidmg inside pan, weigh from 400 to 600 lbs. 



Us«al Prftctloe of CoMdnlt fTork. 

Manhole walls, where built of concrete are generally 8 to 12 inches tfaiek, 
made of Portland Cement concrete, using, 1^ inch stone, mixed in the pro- 
portion of an 1-2-5 and in some iiutances as high as 1-3-8. While in some 
cases the conduits proper are surrounded with Portland Cement oonorete, 
the usual ^actios throughout the countrv is with casing of hydraulio 
eoncrete m a 1-2-6 mixture, stone f inches to 1 inch. 



Tlie Cost of CoMdoits. 

(A. v. Abbot in Eledrical World <md Enginmr.) 

The items of cost of conduit construction are: 
1. Duct material. 2. Pavement per square yard. 3. Street 
tion per cubic foot, including the removal of paving, the refilhnent of the 
excavation sJFter the ducts are laid, and the tonporary replacement of the 
paving. 4. Concrete deposited in place. 6. Linbor of placing duct ma- 
terial 6. Engineering expenses. 7. Manholes. 8. Removal of obstadsi- 



TASXiB ITo. 1. 
Cost of H»aliolos In I»oll»ra. 

A, Briei with Brick Roqf, 







Bate (Dollars). 














Item. 


Amount. 




Min. 
Amt. 


Per 
Ct. 


Av. 
Am. 


Per 
Ct. 


Max. 
Amt. 


Per 








Ct. 






Min. 


Ave. 


Max. 


1 


12.6 


$ 
11.26 




S 




Excavation 


376 cu. ft 


.02 


.03 


.04 


7.60 


11.8 


15.00 


11.2 


Concrete . 


.7 yard 
2200 


6.00 


7.00 


9.00 


3.60 


6.9 


4.90 


6.3 


6.O0I 


4.4 


Brick . . 


12.00 


16.00 


18.00 


28.40 


44.6 


33.00 


35.3 


39.60 


294 


Covsor . . 


1 


6.00 


10.00 


16.00 


6.00 


8.4 


10.00 


10.6 


16.00 


11.2 


Iron . . . 


500 lbs. 


.016 


.03 


.06 


7J60 


12.6 


liJOO 


16.1 


26.00 


18.6 


Repaving . 


6 vards 


.76 


2.00 


4.00 


4.50 


7.6 


16.00 


12.8 


24.00 


17.3 


Cleaning . 


10 loads 


JSO 


.76 


1.00 


5.00 


8.2 
100.0 


7J50 
93.66 


8.1 


10.00 


7.4 


Totals . . 


. • • . 


m « 


• • 


■ • 


60.40 


100.0 


134.00 


100.0 



COST OF UMOERaROirND CONDUITS. 



303 



B. Brick with Qmcrtte Ro4tf. 



Item. 


Amoimt. 


Bate (Dollars) 
Per Unit. 


Min. 
Amt. 

$ 


Per 
Ct. 

14.8 

18.7 

37.8 

9.0 

8.9 

9.9 


At. 

Am. 

• 


Per 
Ct. 


Max. 
Amt. 

• 


Per 


Min. 


ATe. 


Max. 


Ct. 


ExetTation 
CoDcrete . 
Bilek . . 
Corer . . 
Bspavlng . 


375 on. ft. 

1.9 yards 

lOOO 

1 
6 yards 
10 loads 


.02 

6.00 

12.00 

5.00 

.75 

.60 


.08 

16.00 

10.00 

2.00 

.75 


.04 

9.00 

18.00 

16.00 

4.00 

1.00 


7.60 
9JS0 
19.20 
5.00 
4JS0 
5.00 


11.96 
13.80 
24.00 
10.00 
12.00 
7.60 


14^ 
17.0 

aos 

12.8 

16.4 

9.5 

100.0 


15.00 
17.10 
28.80 
15.00 
24.00 
10.00 


18.8 
15.7 

95.7 

13.8 

21.9 

9.1 


ToUb . . 


. • • . 


• ■ 


• • 


• . 


60.70 


1004) 


78.06 


100.90 


IOOjO 







C 


Ctmerete, Manhole, 












Itsm. 


Amount. 


Bate (Dollars) 
Per Unit. 


Min. 

Amt. 

f 


Per 
Ct. 

16.8 
60.6 
11.2 
10.2 
11.2 

100.0 


At. 

Am. 

• 

11.25 
31.60 
10.00 
12.00 
7JJ0 

72.26 


Per 
Ct. 

15.6 
43.6 
13.9 
16.6 
10.4 

100.0 


Max. 

Amt. 

• 


Per 


Min. 


Are. 


Max. 


Ct. 


KxesTation 
Goocrete . 
Cow . . 
BcpsTing . 


375 en. ft. 
4J> yards 

6 yards 
10 loads 


.02 
BM> 
6.00 

.75 


M 

7.00 

10.00 

2X0 

.75 


.04 

9.00 

15.00 

4.00 

1.00 


7.60 
22M 
5.00 
4JM) 
5J0O 


16.00 
40.60 
16.00 
24.00 
10.00 


14.8 
38.8 
14.4 
23.0 
9A 


Totals . . 


.... 


. . 


• ■ 


. . 


44 JO 


104UI0 


lOOX) 



Wl>ene v cr praetioable, a sewer connection to each manhole is desirable 
to provide exit for street drainage. Such sewer connections are essential 
is sli esses wfaAre manholes are equipped with Tmtilating covers, otherwise 
the insnboles will fill durins every storm. 





Gm8 ef Saw 


•r G*«M«cti«Ba IH Dollan. 










Bate (Dollars) 














Itsra. 


Amonnt. 


Per Unit. 


Min. 


PAr 


Ave. 


Per 
Ct. 


Max. 


Per 


, 


Amt. 


ct. 


Am. 


Amt. 


Ct. 






Min. 


Ave. 
.03 


Max. 

.04 


$ 


• 


1 


SsesTstion 


826 ca. ft. 


.02 


4 60 


36.1 


6.76 


26.0 


9.00 


21.4 


Oooerete . 


6 yards 


.76 


2.00 


4.00 


3.76 


29.2 


10 00 


38.8 


20 00 


47 


^ • 


1 


1.00 


2.60 


4.00 


1.00 


7.6 


2 60 


19.6 


4 00 


9 3 


Oorer . . 


16 feet 


.04 


.07 


.10 


.64 


6.0 


1.12 


4 4 


1 60 


3.6 


Beparlng . 


2 loads 


.60 


.76 


1.00 


1.00 


7.6 


1 60 


6.8 


2.00 


4.7 


QssBlng . 


1 


9.00 


4.00 


6.00 


2.00 


15.6 


4.00 


15.4 


6.00 


14.0 


Totals. . 


. • • 


• . 


• • 


• 


12.89 


100.0 


25.87 


100 


42.60 


100.0 



( 



304 



UNDERGROUND CONDUITS. 



Bianholee win occur at intervals of from 250 to 6(X) feet, 

the constant cost per conduit foot for this item is obtained by dividilQg tlw 
various manhole costs by the distances between them. 



VAsxa no. s. 



€)mmtitmmt Coet p«r CondaiC Foot for Mfuiholoa Ui Dolli 







Distance between Manholes in Feet. 




260 


300 


860 


400 


600 


Brick manhole with 
brick roof . . . 


Min. 
Are. 
Max. 


.238 
.872 
.636 


.196 
.310 
.427 


.170 
.248 
.384 


.148 
.236 
.336 


.118 
.186 
.268 


Brick manhole with 
brick roof . . . 


(Min. 
{Ave. 
(Max. 


.203 
.300 
.440 


.168 
.260 
.363 


.146 
.223 
.314 


.127 
.196 
.272 


.102 
.166 
.218 


Concrete manhole . 


Min. 
Ave. 
Max. 


.176 
.278 
.416 


.148 
.242 
.347 


.127 
.200 
.298 


.111 
.180 
.260 


.069 
.144 
.206 


Sewer connection 


(Min. 
{Ave. 
(Max. 


.061 
.104 
.170 


.043 
.086 
.142 


.038 
.074 
.121 


.082 
.064 
.106 


.025 
.061 
.064 



Engineering expense will vary from a minimum of 5 cents per oonduii 
foot to a maximum of 12 cents, depending chiefly upon the difficulty of 
the worlc 

The cost of the removal of obstacles is an item impracticable to estimate 
a priori with any degree of certainty, as it is imposdUe to foresee, and 
usually impracticable to ascertain, even with the greatest care, the impedi- 
ments to be encountered beneath street surface. Experience indicates 
that this expense will vary for small subways from 10 cents to 62 oente per 
foot of conduit; for medium-sized ones from 12 cents to $1.10, and for 
large conduits from 15 cents to $2.25. 

The cost of paving is partially dependent upon the number of duets. 
It is impracticable for workmen to perform their avocations in a trench 
less than 18 inches wide, and, therefore, a strip of pavement of this width 
must be opened irrespective of the number of ducts to be installed. 

The cost of repaving will further vary with the kind of paving. In 
Table No. 4, the usual kinds of pavement encountered, the minimum, 
average, and maximum prices per square yard, and cost per conduit foot 
are given. 

Allowing a disturbance of paving for six inches on each side of the trench, 
the cost per lineal foot for small conduits will varv from 2.3 to 26.3 cents; 
for medium-sized ones from 4.6 to 29.2 cents, and for large conduits from 
6.0 to 35.0 cents. 

Similarly the cost of excavation is only partially dependent upon the 
number of ducts. 



^ 



COST OJ" PAVING. 



306 



i 



a 

I 



I 

h 

I 
1 

e 
8 

I 
t 



I 






5jH 



§ 






-81 



? 






l.i 



I 



■31 

6« 



§ 



SSI" 



I 



P4 






S>188858S8 



CO 



' s 



s 



S 8 S 8 8 » ^. 

eO M 99 pm ci ^ 



S1i§§S§§S 



OQ 



§1§iS|g§§ 



Of 



• «■ 



!^ ^ 8 8 8 

c« ei ^ * iH i^' 



8 S f^ 



S*". §§§ISi§ 



9 



§»: §§§§Hi§ 
■ Jf 



cr •••••• • 



IS SS 8 8 8 8 S 

•ii e<i ^' ' ^ 



I 

8 



I •§ -S 



11- 

•a t "" 



« ■ H <D ^ 9 

^ ^ O O « H 






( 



306 



UNDERGROUND CONDUITS. 



Ezperienoe shows that 3 feet 6 inches is a miniroy nn pennisnble deptb 
for the bottom of subway oonstruotion, and that the cost of street excava- 
tion will vary from two to four cents per cubic foot of material excavated, 
including the removal of the pavement, the refillment of the trench, aod 
the replacement of temporary paving. The cost of excavation will, Uwe- 
fore, stand as in Table No. 1. 

Coat of Atreot M^mrnvwiUmm per CoMdvit Foot Ib Doll 





Minimum 

.02 
per Cu. Ft. 


Average 

.08 

per Cu. Ft. 


Maximim 

.04 
perCn. Ft. 


1 to 9 ducts . . . 
10 to 16 ducts . . . 
17 to 26 ducts . . . 


.106 
.160 
.226 


.1075 

.MO 

.8876 


.210 
.830 
.460 



Table No. 5 summarises these constant items; for oondmts of frook one 
to nine ducts, ten to sixteen ducts, and seventeen to twoity-five doflks^ 
giving the minimum, average, and maximum prices of all, together with 
the percentage that each bears to the total. 

Table No. 6 enumerates the probable prices for the varioua forms of 
duct material laid into place, calculated in a manner similar to the precsd- 
ing tables, including a percentage column showing the effect of eara item 
upon the total expense. 



CoMatMit Coat per 


COO«B 


It Foot te Dollars. 




• 


Minimum. 


Average. 


Maximum. 


Item. 


Cost. 


Per 

Cent. 


Cost. 


Per 
Cent. 


Cost. 


Per 
Cent 


1 to 9 ducts. 
Excavation .... 
Paving 


.106 
.0696 


32.6 
21.2 
15.2 
32.0 

100.0 

88.6 
20.2 
12.1 
29.1 


.1576 

.185 

.06 

.25 


23.4 
27.5 
11.9 
37.2 


.210 
.279 
.12 
1.00 


13.0 
17.4 


Engineering .... 
Removal of obstacles . 


.06 
.10 


7.6 

es.i 


Total 


.3245 


.6725 

.24 

.222 

.06 

.28 


100.0 

29.1 

27.0 

9.8 

34.1 


1.609 

.82 
.3318 
.12 
1.10 


100.0 


10 to 16 ducto. 
Excavation .... 
Paving 


.16 
.0645 


17.0 
17.7 


Engineering .... 
Removal of obstacles . 


.06 
.12 


6.6 
6S.8 


Total 


.4145 


100.0 

43.0 

18.6 

9.6 

28.8 


.822 

.3875 
.26 
.08 
.35 


100.0 

82.8 

26.3 

7.8 

34.1 


1.8715 

.46 

.63 

.12 

1.26 


100.0 


17 to 25 ducts. 
Excavation .... 

Paving 

Engineering .... 
Removal of obstacles . 


.226 
.0970 
.06 
.15 


19.2 

28.2 

6.1 

58.6 


Total 


.522 


100.0 


1.0276 


100.0 


2.34 


100.0 









^ 



COST or UNDERGROUND CONDUITS. 



307 



From the data thus ooUeeted, the total cost of a conduit of any riie is 
readily determined by taking first the cost per foot of street for manholes 
and sewer eonnections; second, the cost of the constant street items as 
given in Table No. 6 depending upon the number of duets, aiKl third, 
the ciotX pet duct foot determined from Table No. 6 multiplied bjr the 
number of ducts to be laid, and adding these three items together, giving 
immediatdy the total cost per conduit foot. 



Coat of Sact Hat«rlal 



TABIDS Ma. V. 

te Place IM Oollara. 





Minimum. 


Average. 


Maximum. 


Item. 


Cost. 


Per 

Gent. 


Cost. 


Per 
Cent. 


Ck)st. 


Per 
Cent. 


Hollow brick. 
1>aet material . . . 
PkMing 


.02 
.006 


44.4 
11.2 
44.4 


.035 

.01 

.06 


36.8 
10.5 
52.7 


.06 

.015 

.06 


34.5 
10 3 


Enctsement .... 


.02 


56.2 


Total 


.046 


100.0 

67.6 

2.2 

30.3 


.006 

.06 

.0026 

.0475 


100.0 

60.0 

2.5 

47.5 

100.0 

53.6 

3,4 

43.0 


.146 

.066 
.004 
.07 


100 


Multiple duel. 
Doet material . . . 
Plsdng 


.036 
.011 


46.7 
2 9 


Eneasonent .... 


.015 


50.4 


Total 


.061 


100.0 

62.5 

3.2 

34.3 


.10 

.06 

.004 

.06 


.138 

.08 

.006 

.068 


100 


OeiBeat-llned pipe. 
Cement pipe. 
Wood pulp. 

Dnct material . . . 

Placing 


.04 
.002 


48.2 
3 6 


BDcasement .... 


.022 


48.2 


Total 


.064 


100.0 

98.04 
1.96 
0.00 


.114 

.95 

.0015 

.00 


100.0 

98.0 
3.0 
0.0 


.174 

.06 

.003 

.00 


100 


Creosoted wood. 
Duct material . . . 
Placing 


.04 
.0006 


96.0 
5 


Eoeasement .... 


.00 


0.0 


Total 


.0406 


100.00 


.0615 


100.0 


.063 


100.0 



Cloa* per Conduit Foot ta Cltloa. 



GoBtper 
Trench Foot. 


Number of Ducts. 


2 


4 


6 


12 


16 

$2.76 
2.76 
2.82 
3.13 
2.78 
2.91 


20 


24 


AtlanU . . . 
Louisville . . 
Cfaieinnati . . 
Boston . . . 
Springfield . . 
Brooklyn . . 


$.88 
.89 
.92 

1.06 
.90 
.96 


$1.14 
1.12 
1.18 
1.34 
1.16 
1.21 


$1.43 
1.40 
1.48 
1.65 
1.45 
1.51 


$2.31 
2.29 
2.36 
2.66 
2.34 
2.45 


$3.22 
3.19 
3.26 
3.66 
3.24 
3.39 


$3.53 
3.63 
3.72 
4.10 
3.68 
3.84 



( 



r 



308 



UNDERGROUND CONDUITS. 



m o 
1 • 









iCKI^flOO 



a I S i S 8 



s 






I 



t 



9 

I 



9 

! 



I-^I 



at I g g 8 I" 



to 









8. S9 ^siisi^SsS:: 

i S "'^ ' ^ ^ ^ I 



gS8 SSCiS, 88 ^9 



iS(i«»a 



fr 



^*»| 

^ Q 



S Ss Ssi^isls^sis S89 88 S8 
g '^S si S § 55 g §9*8'- •s^ 












So §9 S8i»88g8i88? 9S3S 88 S^ 



§ g ^^5; s e a 



5* i 



9 J8s SBialsagSsie wa sg s 
a -3 a SB I g 



e* 



^s«a»- «B« 



J ft 



S S^S l8§»§^§8§Sigl S38S 88 ^& 



fWl«fc« '^IQ*^ 









§ § 



9 S t: - 8 



2^ 



8 g s •• g 






S 



t»t« •<< 



S 

to 

a 



s 









.•a 

' o 



•w 



S 5J «^^5»iSts5^«| til? 

OHOHOHOHUHOH OHO 



S 



^ 



HO 



2. 



•I ' -a 



.& 



••d 



•d 

* 'a 

fl 






4f.d 



a •2'-* 



•a 



e<8 



|S 



^_ -||^ r^ ^- 



'8. 

m 
•'O 

3 



I 









O 

.4 



Za 



t 

•3 



§ 



& 






^1 



« 

3 



9 
3 





A 

a 

a 

M 
P 

1 

e 





a 



.8 



9 
Ok 



► 



^S^Z!!^;::? l: '» «°U mu.t«(iij(; ae pr«ilce of the Boitoii KdUon 
W NBi oc muuiolea mud otcondulu. ——».■«■)( iwiu- 




1 



noi. Suidt. HubolM. 



310 UNDBRGS 




^ 



WiM 



Fio. E>. Plan and 



Fro. e. Pm 




i 





MMA-^-A 


Wl* 


Hf\ 




r*Ti .■ 


^flilft 


1 




1 



Fia. T. Tmufornier Huiliola. 



312 



UNDERGROUND CONDUITS. 




Street Ljvl 




Fza« 8. 





Fio. 9. Gest'B Patent Manhole Deslgni. 




i 




•to. 10. Sootlon*! Vleir of Mmholo Coxers, 



r 



314 



UNDEBQROUND CONDUITS. 








INNER COVER 



8ld9 



/ ^yvv/^v^ \vy\^Y/\v^vv/v^^^ 






< 



aosQDsaa 



aosoasaa 
aasunsafls 

UOSQQ 

oil 



aasoDSQO 



m 



QDSDasQa 



I 






7 




STREET COVER 



Fig. 11a. Manhole Corers. 



TIGHT COVER FOB MANHOLE. 815 




i 



316 



UNDERGROUND CONDUITS. 

li«mls«« Gm« of G««di«tt. 

W. P. HAirCOCK, BOBTOK Edisok Gokpaitt. 



Material and Labor. 



Material. 

Lumbor at $16.00 per M., or .016 cents per 

square foot, B. M 

Concrete at 94.86 per cubic yard, or 18 cents 

per cubic foot 

Mortar at $3.98 per cubic yard, or 14 cents 

per cubic foot 

Ducts laid down beside the trench at $.0602 

per duct foot 



Labor. 

Bzoarate and backfill at 16 cents per hour 

or 9.0278 per cubic foot 

Cut and place lumber at 20 cents per hour, 

or 9>0006 per square foot B. M 

Mix and place concrete at 16 cents per 

hour, or $.0222 per cubic foot .... 
Mix andplace mortar at 26 cents per hour, 

or 9.0026 per cubic foot 

Lay the dnots at 60 cents per hour, or 9*0040 

per duct foot 

Haul away the dirt at 60 cents per hour, or 

9*0142 per cubic foot 

Paye the trench at 91.44 per square yard, 

or 9.16 per sauare foot 

Cost of manholes per duct foot 

_ Total cost of manhol^ __ 490.28 

"~ Total number of duct feet ~" 22,200 
Inspection at 60 cents per hour, or 9'0033 

per duct foot 

Engineering expenses at 9.0214 per duct 

foot 

Incidental expense at 6 per cent of 

total 



Cost 

per Duct 

Foot. 



9 
.0106 
.0231 
.0026 
.0602 



Cost per 
Conduit 

Foot. 

Total 
Expense. 



9 

.1676 

.0390 
.7630 



.0206 
.0004 
.0029 
.0016 
.0040 
.0047 
.0600 



.0221 



.0033 
.0214 
.0116 



9.2350 



.0060 

.0436 
.0240 
.0600 
.0706 
.7600 

.8316 

.0486 
.8210 
.1740 



93.6260 



Total 
Coat for 



Itomfbr 

the Total 

Une. 



9 
.10 
614.16 

68.90 
1U4.4I 



9.31 
6S.48 

37.09 

88.00 

104.7S 

1109.S8 

400.28 

73.26 
476.08 
948.22 



96218.78 



Camt of 5' X *' X »' MaMliol*. 

W. P. Hancock, Boston Edison Compakt. 

28.76 cubic feet concrete, cost in place 9.202 per foot 9J.2 

2,500 hard sower bricks, cost $9.00 per M ».W 

If S. 6' trap and connections cost 5.W 

30' 6' Akron newer pipe, cost 30 cents per foot. . . . . • ,. ... 9.W 
R. R. steel (60 lbs. to the yard), 8 pieces 6' 4' k>ng (1013 Iba) 

cost 9.0126 per lb IJg 

H yards mortar, cost per yard 93.08 •••••• *•:! 

1 manhole frame and cover, 962 lbs., cost 9.016 lb H.w 

973.50 



COST OF UANHOLBS. 



317 



We Shan need labor that will ooet^ follows: 
Bxeavate and backfill part of same, ineludinc that for eewer 

oonneetiona, 785 cubio feet, cost $.0378 per foot $21.82 

RtfDovB from street 304 cubio feet of dirt, coat 50 centa double 

load or $.0142 per foot 

Fa;ve 11.08 yarda (includins nuuihole and sewer oonnection), 

ooet $1.44 per yard 

B. 10 hours, cost 40 cents per hour 

n helpers, 10 hours eaoh— 20 hours, cost 15 cents per hour, 



1 

S 



4.30 

16.05 
4.00 
8.00 

$40.07 

Total cost 1 manhole, complete . $122.57 

€:••$ •€ JDmdmwgrammA Cmidiitts la Cklcagv. 

G. B. Springer, civil engineer of Chicago Edison Co., says: 
The differenoe in local conditions, variations in cost of material and labor, 
make it very difi&cult to give a set of figures which will hold good in many 
places or in fact in the same place under different drcumstancss. 

The following table, however, is submitted as a guide in i4>proximating 
the eoet of work of this oharacter as a result of conduit construction cov- 
ering ten years in Chicago. The cost of manholes is not included in this 
table, but is given in the one following. 



Ti*le r^r 



■sati^ Coat 9i CoMdvlt, P»r !»««< Wmmt^ ii 



Kinds of Pavement 


Number of Ducts. 


2 


4 

$.18 
.21 
.22 
.24 
.31 
.43 


6 

$.18 
.20 
.21 
.23 
.28 
.37 


9 

$.18 
.20 
.20 
.21 
.24 
.31 


12 


16 


20 

$.18 
.19 
.19 
.20 
.22 
.24 


25 


30 


No pavement 

Mai'imfif^t^ . . a . . . • . 

Cedar 

Cedar i sen we and granite • 

Graaite reserve 

A^halt and brick reserve . 


$.18 
.24 
.26 
.31 
.43 
.68 


$.18 
.19 
.20 
.21 
.24 
.29 


$.18 
.19 
.19 
.20 
.23 
.26 


$.18 
.19 
.19 
.20 
.21 
.24 


$.18 
.19 
.19 
.19 
.21 
.23 



The foUowinfl^ table contains approximate figures based on conditions 
pKvailing in Chicago, and may be used as a guide in estimating the cost of 
eonduit construction in connection with the table preceding. 



Valblefor 



V«tal Coat of Manholoa Im IMlToroMt 



Kinds of Pavement. 






Sise of Manholes 


in Feet. 






3X3 

$41 
42 
43 

44 

46 

50 


3X4 

$47 
48 
49 

50 
53 

58 


4X4 


4X5 


5X5 

$109 
111 
112 

113 
117 

126 


6X6 

$133 
135 
136 

138 
144 

156 


6X7 

$142 
146 
146 

149 
155 

168 


7X7 

$160 
163 
164 

167 
174 

188 


8X8 

$189 
193 
194 

198 
207 

224 


9X9 


No pavement .... 

Crfar 

Cedar reserve 

and granite .... 
Granite reaerve . . . 
Asphalt and brick 


$53 
55 
56 

57 
60 

67 


$64 
66 
67 

68 
72 

80 


$222 
226 
227 

231 
243 

264 



The above figures are based on the same prices for repaving, labor, brick- 
layers, cement and sand, as given in the table for conduit, and upon the 
loflowing unit prices: 

Brick work including labor and material .... $12.50 per cu. yd. 

Conerete tope and bottoms $7.50 per cu. yd. 

Back water gates $6.50 each. 

Bewer grates 30 cents each. 

Sewer connections $12.50 each. 



8?*f ?"»*■ • ■ .• $5.50 each. 

Manhrwe frames and covers 



$15.00 each. 



UNDERaROUND CONDUITS, 



H. W. BnCE IN Electric Club Journal, An 

Attcotlon U tailed (a the oroupinc of duoti uid oona 
OrdiDuily ducU an bunched U«ether uid broucht 
the numhole, w sbown in Fig. 12. Hen tbe <»blei di 
one aide and bkU oD the otber aide of tbn manhole. 
manboJe inUb, Thu deBgn u objectionable lor a 



MBaracked 




Fra. 12. Ordinarj' Type at Ifauhola. 



onduit to dann^ trom Aart-«ircotl 

-„,^ in doee [Hx>xinuty to each other. 

I bendinc every cable •faarply M pdnta A and B 



i™i; 




DNDEBOROUND CABLES. 




no. 15. HaalKita OaaMraatian of 
■ in tha tood\ 



s "tr Lj"ti'' i 



Uihi in tha »i 
K>dtd«n tha a 

La pU« vh« 

{kninElc 15 



dunaeed by ■hort-drcuit *t wiy time. In 
■trufiit through th» muihoJe vitbout bfiud- 

r thg ■urtun of tha Kraund tha ooturtructioD 



VmiBBClMOIJirD CABl 

JMlM Kt placad audi 



DdarKTOi 



dmring 



recent wai*. cbleC 



tTpe of the aolld ijitsnu 1« that In vLlcb the condncCon, properly 
"nd lead aorared and proteeted bjr armor, are laid directly In the 
. pluk that haa been videly adopted In Bnrope- 
^BrawlK^lB" Phua la Uia one Bowir 

mtry. Thli plan ntfliiea the manholi ...._ . 
Ttia eablea are dnTn Into the dneti from manhole 
' ~ ipe that baa bean prevjoiulv drava through tt 

■'^roddlng." Boddlng conaliita of acrewInK one -. -■ 

— — manhole and pnahlng Ihein throogb the duct ontil the 
— end la mcfaed. The rope is atlaehed to thelwt rod and the rods 
vitbdravn from the dneti bringing the rope irltb them, Sometlmealn 
« rf ™i. . ««r ..—1 -i_ i, pngied through the docta. Tha lopa I* 



' Boddlng 
be r 
ii»» rtroda'V 'ia« "iteai'*wlre 



■at generallT adopted 
le duct by a 



i 



r 






320 UNDERGROUND CONDUITS. 

attached to the cable by a mechanical deTice which securely gripe the i 
of the cable. 

Various means of drawing the cables into the dncts are arailed 
depending somewhat on the sise of the cable and the length of the 
hand power, man power with windlass, horses, electric motors and 
eurines being thus employed. 

Types of VnAergTOiuid Cables. —The type of cable employed J 
nndergronnd service varies largely with the reaoirements. VirtnaUy 
nndergronnd cables are lead covered to prevent Injury to the insulatioBl 
moisture, gases, etc. For telephone purposes, lead covered, dry j 
insulated cables are universally used, to obtain low static capacity, 
pases 180 and 188.} For telegraph purposes rubber Insulation (see pagej 
and oil saturated cotton or paper are utilised, as in the telegrl^ph serriflej 
static capacity is not of so much importance, but still cannot always * 
disregarded, especially in high speed telegraph signaling. The eonduo' 
commonly usea in underground telegraph cable Is No. 14 B. ft S. eopi 
having a conductivity of 98 per cent. In the case of cotton fiber or pap 
cable, each conductor is insulated to six thirty-eeoouds (A) of an ii 
outside diameter. The insulating material is thoroughly <med and V 
saturated with an insulating oil or compound. 

for JBlectrIc MAgl^t and Power purposes rubber, paper 
varnished cambric insulation are largely used. (See pp. 174 and 180^ O 
to its high cost, rubber cables are not now in as high demand as ionn< 
especiaUy as oil saturated paper cables appear to be quite as d 
efficient and reliable as ruboer Insulation for high potential work. 

It was formerly the practice to place as many as six lead covered el' 
liffht cables in one duct, but experience demonstrated that this wss 
advisable owing to the difficulty In withdrawing when necessary one 
more cables from the duct without injury to the remaining cables. A baisj 
out In one cable also frequently injured adioininff oaoles in the dsctj 
Present practice favors having onlv one cable in eacn duct, although tiun 
may be several conductors within the lead covering. (See page 185.) 

To prevent burning of light and power cables due to short circuits in ttl 
manholes and other ulaces where the cables are bunched, the cables art 
frequentlv covered with asbestos strips about 3 inches wide and A la# 
thick, well impregnated with a solution of silicate of soda which aofltt 
hardens over the lead. The lead covers of cables carrying altemstial 
currents of high amperacre and low E. M. F. should be bonded or careiw 
insulated in the manholes to prevent sparking and possible conseqiNii 
damage, due to Induced currents In the lead cover of the cables. 

All lead covered cables used on high potential circuits should be prs* 
tected from damage by static discharge by flared ends or bells, that Ir, W 
enlargement of the lead sheath to fully twice the diameter of the lead if^ 
the cable, for a distance of about a foot. The bell should then be T* 
with some good insulating material like Ghatterton (Compound, the 
ductor ends, in case of multiple conductor cable, being carefully separ 

Cable Heads. — To prevent the entrance of moisture to the ends 
telegraph and telephone paper cables the conductors of a short lenm 
(about two feet) of rubber covered cable are spliced to those of the P*PV 
cable. These splices are then Insulated. A lead sleeve is passed over tti 
rubber insulated conductors and the lead casing of the paper cable to vhM 
it is then soldered. The outer terminal of the rubber cable is led lutol 
metal box or head to which the lead sleeve is soldered. The free condneMMj 
are solidly connected to insulated binding posts on the inside of tiie 
which binding posts extend to the outside of the head, thus slving sees 
to the conductors externally. The sleeve and box are then filled wila 
melted rubber compound, the temperature of which must be below tbat 
which the rubber insulation will soften ; otherwiso the rubber will 
seriously damaged. 



^ 



CABLE TESTING. 

BBYUW) BY Wm. Mavxb, Jb. 



The majority of the methods of tests and measurements glFen herein are 
')le to a<$rlal, underground, and submarine cables. 



l||»Ueab] 



Blrect lleflectlom Method, w14b Mirror C^alvanoBsotor. ~ 



SUi method, Fig. 1, is generally used in this country in underground and 
Mbmvine vork. 




CASLt 

FlO. 1. 
s and 6= leads. 

G=galTanometer, Thomson or D'Arsonral, mirror type. 
8zz ihonU for O, osnally A, ,1,, r^. 
£= battery, 20, 60, or 100 chloriae silyer cells. 
R=z resistance box of megohm or more. 
BK= battery reyersing kejr. 
Af =short-clrcnit key for O. 
Vbtt eoanect a to lower contact point of SK, and take constant of O, 
Mriag xiu shunt, and small number of cells, say 6 (depending upon the sen- 
■mieM of €f)t vlth standard resistance J7 only in circuit, b being discon- 
Medssihown. If 6 cells aroused in taking constant, and 100 cells are 
obevedfortest, 

fi«n.».«ft - G deflec. X shunt x i? X «) _ „,^. ^. 
Constant = i^ooo,00O = megohms. 

L jj^'^ obtaining the constant, measure insulation resistance of lead &. by 

' ]"Bi]ig it insteadcf SK to a« disconnecting the far end of b from the caole. 

jwwwlt ihonld be infinity ; but if not, deduct this deflection from the 

;• MBction to be obtained in testing the cable proper. Now connect the far 

uS|>ff & to the conductor of the cable, the far terminal of latter being free. 

2*Bop«a^ir carefully, and observe if there are any earth currents from 

; y csSle. If any, note deflection due to the same, and deduct from bat- 

.JJ'TJMdiiigif in the same direction, or add to it if in opposite direction. 

«m«lreiA with 8K, and close one knob of BK^ using, say, the ^ shunt. 

*pff * few seconds open SK; if spot goes off the scale, use a higher shunt. 

!> Mfleetion is low, use a lower snunt. After one minute's electriflcation, 

Bote the deflection. The result may be worked out from this reading, but 

Qe current should be kept on for three or five minutes longer, and rcMlings 

wen at end of each mninte. The deflection should decrease gradually. 

At the end of the last minute of test, open BK, and allow the cable to 

821 



{ 



322 



CABLE TESTING. 



discharge fully. Then oloee SK and prees the other knob of BK, roTem* 
Ing the battery. After a few moments, open SK, and take readings of dellefr^ 
tions as before. 

The insolation resistance in megohms =" ^°* , 

o X o 

where d is the deflection at a given time, and S is the shunt used. If no 



shunt is used, x >« 



constant 



Note that in the aboye constant, the ordinary constant is multiplied bjSQ 
for the reason that the battery is Increased 20-fold, or 6 :: 100. In ease tiie 
same battery is used for testing as for obtaining the constant, then 

G deflec. X S X li 



constant 



1,000,000 



InavlaMaC Cable EnAs for Teato.— Much care must be employed 
in order to insure accurate results.in measuring insulation resistance. The 
ends should be well cleaned and thoroughly dried. For this purpoae they 
are sometimes immersed in boiling paraffin for a few seconds ; or the 
ends may be dried by the careful application of heat from an alcohol lamp. 

If there be no earth currents, the readings with opposite poles of battevr 
to the cable should not varv appreciably at any j^yen minute. Pronooneed 
yariation between the readings at given times and unsteady deflections Indi- 
cate defective cable. 



Ijnavlattoa ]ieaiatauic« by Method of 



of Chaive« 



The insulation reslstuioe of a cable or other conductor having considera- 
ble capacity may be measured by its loss of charge. Iiet one end of the 
conductor be insulated, and the other end attached to an electrometer, in 
the manner shown in Fio. 2. 




Fio. 2. 

Let J7 := Insulation resistance in megohms per mile. 
C= Capacity in microfarads per mile. 
E r= potential of cable as chained. 
e = potential of cable after a certain time. 
Depress one knob of key iC, and throw key K' to the right, and chuge the 
cable for one minute ; then throw key K' to the left, thus connecting the 
cable to the electrometer. Note the deflection J7. Noting the movement <4 
the spot for one minute, take reading e at end of minutCi then 



J?= 



26.06 
Clogf 



If an electrometer is not conveniently at hand, use a reflecting galvanom- 
eter, and after charging cable as before, take an instantaneous nlBchargg. 
noting deflection E due thereto. Becharge cable as before, then open JT 
and at end of one minute, the galvanometer having been disconnectea from 
cable in the meantime, take another discharge-reading of cable, and ^pply 



CABUD8. 



323 



the SUM formola m before. If a condenser of low eapaeity be Inserted be- 
tween P and thegalyanometer, the latter need not be dlseonnected. The 
adTantage of the use of the electrometer is that the actual loss of potential 
of the cable may be obserred as it progresses. 

VMttar Y^iBte It Cable* b J Claric's KetkadL 

In the flgnre (FlG. 3) the letters refer to the parts as follows : 



=rB 




Fio. 3. 

li a high-reelstanoe mirror galvanometer. 

Aitthediant. 

^ ii the shortHsircnlt key. It may be on the sbnnt box or sepaimte. 

Xr U a reversing key. 

Ju/ii a discharge key. 

B iba battery, nanally 100 eella chloride of silrer. 

Ch s ) microfarad standard condenser. 

The jmnt to be tested Is placed in a weU-insulated trough, nearly filled 
vlth lalt water. A copper plate attached to the lead wire is placed in the 
vtter to ensure a good connection with the liquid. The connections are 
ottdeat shown in the figure, one end of the cable being free. To make test 
ekMX^/forahalf minute; then release it^rst depressing one knob of 
^ ^#)f (herebv dischazwing the condenser C, through the galvanometer, 
vA note the denectlon, if any. A perfect piece of cable of the same length 
at the Joint is then placed In the vessel, and if the results with the joint are 
praetieally equal to those obtained with the perfect cable, the joint is passed, 
wboi the direction is very low, it is evident that the joint is sound, and it 
Bay then be considered nnneoessary to compare it with the piece of cable, 
it ii Twy important that the trough and apparatus be thoroughly insulated. 




' Ketlaod. — This method possesses the advantase that 

it dispenses with a condenser, and thereby avoids possible misleading re* 
ralti doe to electric absorption by that instrument. The connections for 
A« «>eetrometer test are shown in the accompanying figure (Fig. 4). 



{ 




ELECTWMIETEa 



( 



ltd. 4. 

B is a battery of about 10 cells. 
^j is a batteiy of 100 or more cells. 



324 



CABLE TESTING. 



As in the preoedins test, it is here Mghly essential that the insulation ef 
the trough should be practically perfect, or at least known, so that if not 
perfect, proper deductions may he made for deflections due to it alone. 

To test the insulation of the trough, depress K„ and close switch S, Thk 
ehaiges the quadrants of the electrometer, and produces a steady deflectlai 
of its needle, and shows the potential due to the small battery B. Now 
open switch S, still keeping a^ closed, and watch the deflection of needls 
for about two minutes. IS the insulation of the trough is not perfect, thert 
will be a circuit, so to speak, from the earth at the trough to the eaitk 
shown in the flgure, and a fall in the deflection will be the result. If, hov- 
erer, the drop of potential is not more than is indicated by a fall of two cr 
three divisions, the insulation of the trough will suffloe. The electrometer 
is discharged by closing switch 5. which short-circuits the quadrants, K, 
being open at this time. The loint is now connected as in the figure. 
Switch S is opened|and key K„ depressed, thus charsing the joint with the 
large battery^,. This produces a quick throw of the needle, dne to the 
charging of the Joint. Next, keeplng/f^ closed, discharge the electrometer 
by closing switch S for a moment. The switch is then opened, and If the 
Joint is imperfect as to its insulation, the deflection will rise as the e]ee> 
tricity aocuniulates in the trough. The deflections are recorded after one 
and two minutes, and are compared, as in the previous test, with a piece of 
perfect cable. The results obtained with the Joint should not greatly a- 
ceed those with the cable proper. 

Capacity tests are usually made by the aid of standard condensera. Con- 
densers, or sections of the plates of condensers, may be arranged in parallel 
or in series (cascade). 

AmMiC«aneM« of GoBdeaaera— Parallel.— Join like terminals 
of the condensers together, as in the flgure : then the Joint capacity of the 
oondensers Is equal to the sum of the respectlTC capacities. 

Capacity, C=z € + €,-{- e„ + c,,„ 



X 



X 




x-~i 



z 



»w l 



Fig. 6. 
CoBd«Ba«n la Aertea or Caacado. — Join the terminala, as la 
Fig. 6. The total capacity of the condensers as thus arranged is equal to 
the reciprocal of the sum of the reciprocals of the several eapaoitlea, or 

1 

Capacity in series = lil..J_.JL 

FlO. 6. 
Condensers are now constructed so that these two methods of arranging 
the plates of a condenser mav conveniently be combined in one condenser, 
thereby obtaining a much wider range of capacities. 



1 



CABLES. 



325 



CapacHj kj IMrvct lMwlui>S«.— It iB ftMiumitly d^ 
ilnMe tolmow the eafMoity of » oond«iiaer, a wire, or a cable. This may 
be awertaiaed by the aid of a standard oondenaer, a trigger key, and an 
attatte or ballistio galTanometer. First, obtain a conttarU. This is done by 
■otiBg Uie deflection d, due to the discharge of the standard condenser after 
s eiisi|s of, say, 10 seconds from a giTcn E.M.F. Then discharge the other 
eoadeoMr. wire, or cable through the galvanometer after 10 seconds charge, 
•■d note IM deflection df. The caitacUy e' ot the latter is then 

c hdag the ci^MwIty of the standard condenser. 

GnyfBcHy ^y TIiobmom** Metk««.— This method is 
'tsln 



■eeonte results 



used with 
testing the capacity of long cablet. In the flgnre (Fig. 7) 




l=- ukthI 



I 





FlO. 7. 

'= battery, say 10 chloride silrer cells. 
t= adjustable resistance. 
B= lized resistance. 
ttiritalTanometer. 
C zz atandard condenser. 
1,2, 3, 4, 5, keys. 

To (Mt, eloae key 1, thus connecting the battery B. through the resist- 
•Be«B£,A^ to earth. Then 

F: r,::R:E, 

vWa Fand F, = the potentials at the innctions of the battery with Jt Jt^. 

Next close keys 2 and 3 simnltaneonsqr for, say 6 minutes, thereby char- 
M the condenser to potential V. and the cable to potential V, 

l«t Cbe the eapacitv in microfarads of the condenser, and C, capacity of 
cable, and let Q and Oy be their respective charges when the keys were 
*•?!??: '^^^ Q:Q,::VCi V,C,. 

Open kejB 2 and 3, keeping key 1 closed for say 10 seconds, to allow the 
cBargee of cable and condenser to mix or neutralise, in which case, if the 
eif^ ve equal, there will be no deflection of the galvanometer when key 
«« eloied. If there is a deflection, it is due to a preponderance of charge 
n Cor Cf. Change the ratio of it to jR^ until no deflection occurs. 

■nwn. VC= V, C, 

Batwefoond V,\V\\R,\R 

•^ C,-=z% C microfarads. 



( 



( 



326 



CABL£ TESTING. 



CapAcMor 1»7 Cl«tt*« H«tk«d.-~Fic. 8 ahowB the oooaeeikMM far 

teBtiuff the influlation of » cable by this method, whidi ie oonndered m»ii»> 
whatbetter than Kelvin's, aa it does not necessarily require a well insulated 
battery. 

First adjust the resistances R and Ri to the proportions of Ci to C. ss 
nearly as may be, by moving the slider 8. Depress K for five aeeonda, 
which will charge both cable and condenser. At the end of the time, de- 
press k and observe if there is any deflection of the galvanometer O. If 
there be any such deflection, open k again, let up the key K, and shori- 




55 

miiiiiiiii 



? 



*\AJv%A^>A/WW^^^^>/\^N^>5|r^/N/v 



L ^(2Pi c.ini 




Ocound 



\ 



Fio. 8. Qott's Method of Cable Testing with Condenser. 

eirouxt the condenser Ci with its plug for a short time, then readjust R and 
Rt and repeat the operation until there is no deflection of the galvano- 
meter O; uien 



C I \j\ I I iC% I K 



and C - ^ C,. 



llie best conditions for this test are when R and R^ are as high as poiH 
sible, say 10,000 ohms, and C| and C are as nearly equal aspossible. 

X«stiBr Capacities by I.ord M.elvte*s I»ead-S«ttt, M«Ui- 
oelliil»r Toltmeter. — Suitable for short lengths of cable (See Fig. 9.) 

MV ■■ multicellular voltmeter. 
ilC -• air condenser. 

B-" battery. 

iS— switch. 

Qoi total charge in condenser and Af V, due to battery. 
Ca — oapaci ty oi AC. 
(76— capacity of cable. 

First dose switch S on upper point 1 and charge MV and AC to a desired 
potential, V. Next move switch S from point 1 to lower point 2, and note 
the potential V, and MV. 

Then Q' - V (C+ Co)= KCC + Ca + Cb). where r in the capacity of volt- 
meter. Ordinarily C can be neglected, as comparea with the capaoitiea of 
AC and the cable, in which case, by transposition, 

C6-(y-7/)Ca- V,. 



1 



CABLES. 



327 



OondueUNrB of telephone cables are measured for eapaoity with the lead 
•heathinc of annor and aU oondoetois but the one under test grounded. 




Fio. 0. 



_ Brealca la Calll«e or OT«rlam4l Wiroa by Capa- 
city Tm t aT — When the capacity per mile or knot of the oonouotor of a 
cible ia known ita total capacity up to the break ia measured by comparison 

Ma 

with a standard oondenaer. Then z^ —,, x being distance to fault in miles, 

m 
sr espseity of eondncCor per mUe and m total oanacity of conductor from 
the testing station to break. ▲ dear break in the cable or conductor is 



la GalblM or Aairlal ^iTtvaa^-Ptof. Ayr- 

■To locate the oross at d (Fig. 10) arrange the connections 




'tfTnnr 




Fio. 10, 

•tihown. This Is ylrtnally a Wheatstone bridge, in which one of the wires, 
a, Is one of the arms of same. Adjust r until a (« + y) = ftr, when r will be 
HWl to a 4- y , if a = ft. 

d 




{ 



I 



Fig. 11. 



328 CABLE TESTING. 

Next eonnect the hattery ^ line m fnatead of to earth, as In Ills. 11, 
adjust a until ax = by. 

X h 

and as X 4- y = r in the first arrangement, 

henee, « = j-j-^. 

This test may he yarled hy transposing O and the battery, in Fig. 9, whUk 
is the old method of making this test. 

liocatlnr S^nlte !■ Aerial inr«a •w Cablea bj «li« 
Test. — Two conductors are necessary for this test, or both ends of a 
must be available at the testing-point. Also it is assun^ there is bat 
defect in the conductor. The resistanoe of the fault itoelf is negligible la 
this test. 

Measure the resistance L of the loop by the ordinary Wheatstone bridss. 

Morraj Metbod.— Connect as in Fig. 12, in which a and 6 are the 
arms of a wheatstone bridge, and y x are resistances to fault, the eondao- 
tors beins joinedat J'Cin the case of aerial wire, for instance). Gloeekey 
and note the deflection of needle due to E.M.F. of chemical action at faalK 
if any. This is called the false sero. 




Fio. 12. 

Now applT the positive or negatire pole of the batteir, by depressing one 
of the knobs of rerersing key A*, and balance to the false seropreTioosly 
obtained by varying the resistance in arms a or 6. Then, by wheatstone 
bridge formula,- 

axzz hy, 

and l = x -\-y 

y=zl^x 

« = r—.l 

a-\- b 

y = p-r L 

To ascertain distance in knots or miles from 2 to ^, divide x by resistanos 
per knot or mile ; to ascertain distance from 1 to /^, divide y by resistance 
per knot or mile. 

The foregoing test is varied in the case of comparatively short lengths of 
cable, in the manner shown In Fig. Idy in which the positions of the battery 
and galvanometer are transposed. Otherwise the test and formula are the 
same. It is advisable to reverse the connections of cable or conductors at 2 
and 1 , and take the average of results obtained in the different poeitloot. 
In this latter method, battery B should be of low resistance, and well insu- 
lated. 

Best conditions for making test, according to Kempe. — Resistance of ( 
should be as high as necessary to give required range of adjustment in a 



"^ 



CABLES. 



329 



9 of SBlvAnometer should not be more than about five times the 
of the loop. 




Fia. 13. 

Tari«7 Mj^mp T«flt. — Measure resistance of loooed cable or oonduo- 
ton as before. Then connect, as shown in Fig. 14, in which r is an adjustable 
ifBstanee. If currents due to Ifault be present, obtain false sero as before. 
Thai dose key K, and adjust r for balance. In testing, when earth current 
IB pRMnt, the best results are obtained when the fault is cleared by the 
MtpLtire pole, and just before it begins to polarise. 




Fio. 14. 



Then 



X — 



L -r 



«We X fa the distanee of fault, in ohms, from point 2 of cable proper. 

Tbeo X •+■ by the resistance of the cable or oonduotor per knot or mile 
Vnt ths distanee of fault in laiots or miles. 

When the resistance of the **good" wire used to form a loop with the 
«f«etive wire, together with that portion of the defective wire from J to F, 
a leM than the resistance of the aefeotive wire from the testing station to 
wilt, the resistanoe r must be inserted between point 1 and the good con- 
<iiutor, the defeotive wire being connected directly to point 1. The formula 

i> thii ease is x "- — x — . x, as before, bang the distance to fault in ohms. 



Vb localise Wmmit wliea lieeleiaBc* of CoMdvctor ie 
u«WBMiA a Paralleil CFo«d Wlr« ieMot A Tafllable.^ Measure 

'>J Wbeatstone bridge resistance (r) from A to earth through fault F^ and 
f^iiBtuice (r^ from A' to earth through fault, Fig. 16. Let li be resistance 
of coodnetor from Aio A'^* the actual resistance of conductor from A to 
' and y actual resistanoe of oonduotor from A' to F, 




i 

( 



« — 



R +r - f 




330 CABLE TESTING. 

and V- 

in ohma, from wfaioh th« datanoe in feet or miles may be oaloulated. 



A R A 



r 



Fn. 16. 



r 



liOCAtlar Faalte im lMMa»t«d fTliwe.— The following. w» (o 
speak, ** rule of thumb," or point to point electro-meehanical meiliodi of 
locating faults in unarmored cables, in which the defect is not a prononnoed 
one, haye been found snccessf ul. 

fFarr^B'a BIetli«4«— The cable should be coiled on two insulated 
drums, one-half on each drum. The surface of the cable between the dnuns 
is carefully dried. One end of the conductor is connected to a battery which 
is grounded. The other terminal is connected to the Insolated quadrants 
of an electrometer, the other pairs of quadrants of which are connected to 
the earth. Both drums being well insulated, no loss of potential is obeerred 
after three or four minutes. An earth wire is now connected first to one 
and then another of the drums, and the fault will be found on the drmn 
which shows the greater fall on the electrometer. The coll Is now uncoiled 
from the defectiye drum to the other drum, and tests are made at Interrali 
until the defect is found. 



F. J'ttcob coils the core from a tank to a drum. The battery is 
nected between the tank and the conductor, one end of whidi is free. A 
galvanometer is joined between the tank and drum, which need only be 
partially insulated. The needle shows when the fault has passed to the 
drum, and it can be localised by running the galvanometer lead lUons the 
insulated wire. 

Copp«r Keeletence, or CwBdnctlTlty of C»blea« 

The copper resistance of the submarine and underground cables used in 
telephony and tdegraphy is always tested at the factory, usuallv by the 
Wheatstone bridge method. In such a case both ends of the cable are ac- 
cessible. Whcb the cable is laid, if the far end is well grounded, the oop- 
per resistance may be measured, either by the Wheatstone bridge meCliod, 
or by a substitution method, as follows: First, note the deflection due to 
copper resistance of conductor. Then substitute an adjustable resistance 
box and vary the resistance in the box until the deflection equals that due 
to cable. This latter resistance is the resistance of the cable. If there are 
earth currents on the cable, take readings of cable resistance with each 
pole of battery. Should there be any difference between the results 
obtained with the respective poles of the battery, the actual resiatanee 
will, according to F. Jacob, be equal to the hannonic mean of the two 
results, i.e., 

where R is the actual resistanoe, r is the resistance with •(• pole, i' is the 

resistance with — pole. 

To measure copper resistance of conductors by the voltmeter, first 
measure the E.M.F., V of testing battery. Then place the voltmeter in 
series with the battery and conductor or instrument to be tested| exactly 
as a galvanometer would be placed, and note the deflection V in volts. 
It win be less than in the first instance. Unknown resistanoe z will be 
found by the formula: 

where r is the resistanee of the voltmeter ooiL 



CABLES. 331 



Tk«» C«re of the cable, that Is, Uie insulated oopper conductor, Is 
made, as a rule, in lengths ox 2 knots, which are coiled upon wooden drums, 
ind are then immersed in water at a temperature of 76^ F. for about 34 
boTm. The coils are then tested for copper resistance, insulation reeia- 
tanee. and capacity ; the results of which tests, together with data as to 
length of coils, weight, etc., are entered on suitably prepared blanks. 

iJter the tests of some of the coils have been made, the Jointing upof 
the cable begins, which Is followed by the sheathing or armoring. The 
jotntB are tested after *24 hours immersion in water. I>uring the sheathing 
. proeeM, continuous galvanometer or electrometer tests are made of the 
core, to see that no Injury befalls the cable during this process. In fact, 
pnctkally eontlnuous tests of the cable for insulation resistance, copper 
rcaiitaiice. and capacity should be made until the laying of the cable b^ins. 

During laying, the cable should be tested continuously, and communica- 
tion ihonld be practically constant between the ship and the shore. An 
anangsment to permit such tests and oonununioation is shown in Fig. 14. 




OABLt 



V//////////y///y 




Fro. 10. 

hi tUs ^ure, Oi is a marine galvanometer, B is a battery of alx>ut 100 
Mb on dup-board. In the shore station, L is a lever of key JiC, C is a con- 
t^eoiw, 0} IS a galvanometer. Normally key K is open and the cable is 
charged hy battery B, If. while the cable is beinjg paid out a defect occurs 
ia the insulation, or if the conductor brealcs, a noticeable throw of the galva- 
ooneter follows, and the ship should be stopiied and the cause ascertained. 
By pr^arrangement the lever of shore key K is closed, say every 6 minutes, 
thereby charging the condenser C, which causes a tnrow of the galvano- 
neten' needles. If the ship or shore fails to get these periodic sipials, or 
if they vary as to their strength, it indicates the occurrence of a defect. 
At the end of every hour the snip reverses the batterv, which reverses the 
weetkm of the deflection of the galvanometers. Ii the ship desires to 
mnnumieate with the diore, the battery is not reversed at the hour, or 
» ravened before the hour. If the shore wishee to speak with the ship, the 
W JT is opened and closed several times in succession. In either event 
with eonneet in their regular telegraphing apparatus for conversation. 

Gmap^uiid CablttSt that is, cables of more than one conductor, have 
their eonductora connected in series for these tests. If there is an even 
umber of conductors, two of them must be connected in parallel. 

ittefT Faolta la VsAerrroaad Cables. 

-. .^..v.-.^ • ..^ult in a c 
dowtive conductor and 




Iiocatiair Faalta la VaAerrroaad Cables. A 

TV> loeaHse a fault in a conductor ol a cable, form a loop consisting of the V 

u*f«tive conductor and a x'^A i 

VMd conductor of equal resis- ^ { \\ 

tanoe and length, with battery / V"/ 

* a •hown.Tig. 17. Place y 




>n ammeter in each leg of 

«»p \' If current in leg A — ^ ^ / a \" r 

to fault F ia /, and current .r— . E ^'•*— { T ) i 

»nleg/'tofaultis/':Pbeing T vLy I 

^b of loop L and X the i 4 

«««M»fiain A' to fault J?, ^ ^ 

Fro. 17. 



332 



CABLE TESTING. 



then 



/' 



D-x 



andz — 



IL 



The compttM method of locating faulte in underground cables oonaista* 
briefly, in sending a constant continuous current of about 10 amperes infco 
the cable through the ground, the current first passing into an automatie 
reverser which reverses the direction of the current flow every ten seoonda, 
A manhole is then opened near the center of the cable length and a pockeC 
comnass laid on the lead sheathing of the faulty cable and observed for 
say naif a minute. If the ground is further from the source of reversed 
current the compass needle will swing around approximately 180^ upoA 
every reversal at the end of each ten seconds interval. The manhole m 
immiediately closed and another opened, say a mile further away from the 
source of test current, and if no motion of the compass needle occurs, then 
the fault has been passed and another manhole is opened between the two 
first positions, and so on until the fault is finally located in a section be- 
tween two manholes. H, O. SUM, in Trans. A. /. E. E, 



Hirli V»ltace or IMelectric Teato of CaMm or OOMr 



Gables intended for high pressure circuits ranging from 500 to 60,000 
volts or more are usually tested at the factory to ascertain their ability to 

withstand specified voltages. For 
the lower voltages the cables are 
^netallv tested for three or four 
times the contemplated working 
pressure. For higher voltages the 
cables are usually tested for one and 
a half to twice the working electro- 
motive force. iSss ttandcardiaoHon 
ndeBofA.I.E.B. The present limit 
for undernound power cables is 
about 30,000 volts. The alternat- 
ing electromotive force for these 
tests is supplied by specially de- 
signed step-up transformers, which 
must be of suflSdent kw. capacity 
to supply the charging eurrent called 
for b^ the eable to be tested. The 
charging eurrent varies directly as 
the frequoicy, directly as the 
E.M.F.. and aireotly as the statio 
capacity, and as apparent enercr 
(Skintter. EUdrical Age, Julv, 1905) 
is equal to current multiplied by 
E.M.F., the apparent output of the 
transformers reauired must vary 
directly as the frequency, directly 
as the square of the E.M.F., and 
directly as the static capacity in 
microfarads of the cable or apparatus under test. ^ For example an under- 
ground cable having a statio capacity of one microfarad, and tested at 
20,000 volts, 60 cycles, requires a testing transformer of 160 kilowatt capao- 
ity; tested at 40,000 volts the same cable would require a testing trans- 
former of 600 kilowatt capacity. The testing electromotive force is regulated 
hi several ways, for Instance, by means oi a rheostat in the field of the 
generator, as in Fig. 18, or by employing a number of small transformers 
capable of being connected up, as indicated in Fig. 19, in which the range is 
from 10,000 to 40,000 volts in steps of 10,000 volts. The voltmeter or toI- 




Fio. 18. 




i 



^i 



"o'^.F 



- - -, ioof prinaiT 

er, or the voltmeter may be Disced directly in the 
I m the IntiDjf circuit is Imiueptl^ employed 



've £000 volti. to ■ »ble or 
IK its iiuulHtion. care ihould 
Ignited; And for thia it 'im 
the Intini; truuformer iwd 
try. gsUEiiiE their poinli at 
miltee of elaDdudi d the 
ig the voltmeter « Ibe pm- 
1. what the indicktiou el the 



r rheoet'ta eoniletliis 



1 ailed with w 



r,Duke 



••■b r«r CbKIo E>«i<. — All lead-covered cable end* rboald be pro- 
tected from dAmage bv fltatlo dUcbarga bv Aarad ends or bella, that li. by 
anlarnneiit of the lead ibeath to Fully tv(ce the dlsmeter uf tb* lead over 
the cable, for a dlstaooe of about a fnot. Lead or bran cable headi or 
belli are niDcb Died on the endi of hiib patenilal underinnuid oablea. 
Tbli bell etaonid then be fllled with aome gnod Iniulatlna material like 
Chatterton Compnaod, the eondactor ende, In CAM ol maluple oODdnetor 
(Sblea, batug carefully aeparatad and Brrangad. 



s; 



DIRBOT-CURRBNT DYNAMOS AND MOTORS. 

Rbyibbd by Cbcil p. Pools and E. B. Raymond. 

Bzoept where other deflnltions are ffiyen, the definitions of the Bymlwilfl 
used throughout this section are as f oflows : — 

A = Area in square inches. 

^ = Aggr^ate area of all brush faces. 

; = Magnetic density in armature core body at full load. 
«»= Magnetic density in field magnet core at full load. 

= Average magnetic density over pole-face at full load. 
T = Magnetic density in armature tooth tops at full load. 
1^= Approximate magnetic density in armature tooth tops at full load. 

:= Magnetic density in armature tooth roots at full load. 
/ = Approximate magnetic density in armature tooth roots at full load. 
;r = Magnetic density in armature teeth at a specified point, 
r'rr Approximate density in armature teeth at a specified point. 
= Brush-face dimension crosswise of commutator bars, 
y = Average distance between interpolar edges of adjacent pole-faoes. 
Z>c "=. Diameter of armature core over teeth. 
Dk = Diameter of commutator barrel. 
/)• = Diameter of central hole in armature core. 
Dp = Diameter of pole-face bore. 
Dt = Diameter of circle drawn through narrowest parts of armatare oore 

teeth. 
d = Diameter of bare round wire, in miZ«. 
A = Depth or thickness of winding in a magnet coil. 
3 z= Air-sap length from pole-face to tops of armature teeth. 
S = Total E Jtf .F. generated in an armature. 
Bw = E.M.F. delivered by a dynamo or applied to a motor. 
e = E.MJ?*. at terminals of one magnet coil. 
JF = Ampere-turns per pole required by complete magnetic eircalt at 

full load. 
Fq = Ampere-turns per pole required by complete magnetic olreuit at 

no load. 
Fa = Ampere-turns per pole required by armature core at full load. 
Fg = Ampere-tums per pole required by air-gap at full load. 
Fm ■=. Ampere-turns per pole required by magnet core at full load. 
Fp = Ampere-turns per pole required by pole-piece or shoe at fall load. 
Fr = Ampere-tums per pole required to balance full-load armature 

reaction. 
F» = Ampere-tums per pole in series field-winding at full load. 
J^«A = Ampere-turns per pole in shunt field-winding at full load. 
Ft = Ampere-turns per pole required by armature teeth at full load. 
iV = Ampere-tums per pole required by field-magnet yoke at full load. 
/ = Ampere-turns per inch length of magnetic path at full load : 

Subscripts a, m, p, t and y apply to armature core, magnet core, 
pole-snoe, armature teeth and magnet voke, respectively. 
(7 = Girth or perimeter of a complete magnet coil. 
g = Girth or perimeter of form or bobbin on which a magnet coil it 

wound. 
h = Depth of armature coil slot. 
la = Total armature current. 
Ith = Shunt field current. 
/w = Current delivered from a dynamo. 
i = Current in a specified conductor, or coil. 
«• =r Current in each armature conductor. 
Am = sin (180 ^-^p); hat Dp = chord of polar arc. 
kff = a coefficient ; ib^ £ = increase of air-gap span due to fiux spread. 
i^ = a coefficient ; 1^6=. increase of air-gap width due to flux spread. 
ic» = Number of commutator bars between the two to which the terml> 
niUs of each armature coil are connected. 

834 



NOTATION. 835 

Im = Length of magnetie path In umatnre oore beneath slots. 

1/ = Length of a epeeUlea lield-magnet coll parallel to flux path. 

Lm = Length of magnetlo path in one field-magnet oore. 

Im = Length of magnetlo path in one magnet pole-piece or shoe. 

If = Length of magnetic path in fleld-magnet yoke between adjacent 

It = iStel iisngth of each annatnre oondnotor. 

SI = Number of windings in a multiplex armature winding. 

Jf« = Total number of armature conductors around armature periphery. 

Kk = Number of commutator bars and armature coils. 

^« = Number of armature teeth (and slots). 

m = Maximum number of commutator bars simultaneously in contact 

with one brush at any instant. 
F =Goefflcient of magnetic leakage. 
P^ = Total watts loet m armature. 
f = Total watts lost in armature excluslTe of projecting parte of tha 

winding. 
A = Watts lost at all brush faces. 
P, = Watts lost by eddy currents, 
ft = Watts lost by hysteresis. 
Pr = Watts lost in entire armature winding atone. 
P/ = Watts lost in armature winding excluslre of projecting parts. 
/». z= Watts lost in series fleld-magnet winding. 
P* = Watts lost In shunt fleld-magnet winding. 
Pw = Watts of dynamo armature output or motor armature intake. 
p = Number of fleld-magnet polos. ^ _^ ^. 

= Number of parallel paths through an armature winding : 

NoTK :--In a multiplex lading, q = total paths in all the 
windings. ^ . . 

Jl = Resistance of armature, commutator and brusnes, warm. 
& = Resistance of armature winding, warm. 
JU = Keeistance of embedded part of wrmature winding, warm. 
A =MectiTe resistance of aU brush-face contacts; 7.R» = Volts drop 

at brush faces. , ., . w 

r =: Resistance of a speclfled conductor or coil in ohms. 
r.p.in.=: Rerolutions per minute. 
r.pA = Revolutions per second. 

1 = Width of one armature coil slot. 
T' = Torque in pound-feet. 

T rr Width of one armature tooth at the top. * ^ ^ »« 

I = Wld^ of one armature tooth at the narrowest part, exeept in 

equation 82 and Table V. „.*i^« tM ^^a 

I = NmSber of turns per armature coil ; only in equation 32 and . 

Table V. M 

9j^ =z Temperature rise of armature, Fahrenheit degrees. ■ 

•k = Temperature rise of commutator, ^^o«^\«l* degrees. 1 

•t = Temperature rise of fleld winding, Fahrenheit degrees. ^ 

T = Width of one armature tooth at a speclfled point. 

♦ = MaSetlc flux passing from one pole^f ace to armature at full load. 

♦• = Magnetic flux in magnet core at full load. 

♦» = Magnetic flux In one air-gap at no load. 

tm^ — MAffnetIc flux in magnet core at no load. . 

r = ISS spSn 5- polo-pftch = proportion of armature circumference i 

coTcred by all pole-faces. I 

» = Volnme of iron or steel, cubic inches. ^ 

«• = Volume of iron or steel in armature core body, 

w = Volume of iron or steel in armature teeth, 

r. = Gross length of armature core, between end plates. _ « q ^ 

«. = Net measurement of armature core Iron parallel to shaft = 0.9 X 

/ Wm — ventilating ducts). 

Wh = Width of commutator barrel, parallel to shaft. 

IFp = Width of pole-face parallel to shaft. 

HOTK.— All dimensions are in inches, except wire diameters. 




336 



DYNAMOS AND MOTORS. 



FU]!ri»AMEirTAIJI. 



One Tolt is generated in anelectrical oondootor by tbe *^eiittl]R£'* oC 
100,000,000 maxwells per second. 

One volt 1b generated In a looped or coiled conductor by a uniform Taria- 
tlon of magnetic flux threaded through the loop or coll when the 
rate of change is 100,000,000 maxwells per second. 

Consequently, Uie E.M.F. generated in any direct-current armatnro is 



E=z*N0^r.p.8,l(r* 



(1) 



Dynamos are 



Serles-wound, to dellTer constant current, 
Bhimt-wound, to deliTer approximately constant E.M.F., 
Compound-wound, to deliver strictly constant E.M.F. at some point in 
the work circuit. 



The entire field winding of a series-wound machine is in series ^rith its 
armature, and therefore carries the full current ; an auxiliary regulator is 
required to maintain the current constant under varyins loads. 

The field winding of a shunt- wpund dynamo is connectidd to Its bruahes in 
series with an adjustable resistance (rneostat) : as the load increases, the 
drop in the armature wlndinff and connections increases and the ayailable 
E.M.F. at the terminals is thereby reduced, necessitating adinstment of 
the rheostat to strengthen the field excitation and bring the terminal 
E.M.F. up to normal. 

A compound-wound dynamo ia proyided with a shunt field winding oan- 
nected either to its brushes or to its main terminals, in series with a rheostat, 
and an auxiliary winding of relatively large conductor connected in series 
with Uie armature. The shunt winding excites the machine to normal vol- 
tage at no load ; the application of a load causes the field excitation to be 
strengthened by reason of the current flowing in the series winding. The 
series winding is proportioned to increase the field strength in reeponee to 
any increasein load, to such an extent as to maintain the proper E.M.F. at 
a predetermined point in the work circuit. The rheostat in the shunt field 
circuit is for the purpose of adjusting the no-load E.M.F. within praotical 
limits. 

The relation between fl^d excitation and generated E J!iI.F. is shown by 
the " magnetization characteristic " curve. See Fig. 1. The early part 

of the curve is practically a straiight 
line because the iron or steel in tne 
magnetic circuit has such high perme- 
ability at low degrees of magnetixatton 
that the flux Is almoet directly pro- 
portional to the exciting toree. As 
the iron or steel approaches sat- 
uration, the permeability decreases 
rapidly and a given increase in excita- 
tion win not produce an increase hi 
flux equal to the Increase produced 
by the last previous equal increase 
ill excitation ; hence the sharp bend 
in the curve. In constant-potential 
machines, the magnetic eircmt should 
be proportioned so that at no load 
the characteristic curve has corn- 
intersection of the lines a and e in the 




-TMMt OH PIKLO 

Oil ounmirr w nckM 



Fig. 1. Magnetisation Curve. 



menced to bend sharply, as at the 

diagram ; the lines b and d indicate respectively the total internal E.M.F. 

f generated at full load and the ampere-turns required to produce it, and their 
ntersection establishes the point on the magnetization curve oorreqionding 
tofuUload. 



DYKAMO CHARACTERISTICS. 



337 



Ckaracterintlc— This corro li acurreof regnlto, in 
which the dyiiAmo is excited from its own current, and with the speed con- 
etaat, the terminal Toltaee is read for different values of load. 

The ennres for series, shunt, and compound wound machines all differ. 

The obserratlons are best plotted in a curve in which the ordinates repr»* 
■ant volt values, and abscissas amperes of load. 

Seriu dynamo. In a series machine all the current flowing magnetises 
tbe field, the volts inorease with the current, and if fully developed the 
carve is somewhat like the magnetisation curve, being always below it. 
however, due to the Ices of pressure in overcoming internal resistance ana 
armature reactions. The diagram. Fig. 2 (armature reaction being neg- 
lected), is a sample of 
the external characteristic of a series dynamo. 

To oonstmct this curve from an existing 
machine, the curve of terminal voltage can 
be taken from the machine itself by ariving 
its armature at a constant speed, and varying 
Ike toad in amperes. 

The curve ** drop due to internal resistance," 
sometimes called the " loss line,*' can be con- 
stmeted by learning the internal resistance 
of tiie machine, and computing one or more 
values by ohm's law, and drawing the straight 
hue through these points, as shown. 

The curve of total voltage is then con- 
structed by adding together the ordinates of 
the ** terminal volti^e " and " drop due to 
iatemal resistance." 

A very good sample of curve from a modem 
series machine is to be found in the following 
description of the Brush arc dynamo. 

llg. 3 is * characteristic curve of the new Brush 125-lt. Arc pynamo 




MWUIUUMO 



Fig. S. External Charac- 
teristic of Series Dynamo. 



as 












1 — 


__ 


— 










^~ 


^^ 


^ 


•MO 








/ 


/" 












\ 










CflflB 








z 














> 






































SMO 






























MQQ 






























































4M0 
































«M0 


































f 


























tMO 




J 
































/ 




























mmm 




/ 




























m» 




/ 
























































































uoo 








oHARAOTemsno curve 
vmy^at rkv. pm mm. 










vm 














































MO 
































,f 
































: 


1 


1 


1 i 


1 


\ < 


AM 


r ( 

PCW 


i 1 


> u 


> 1] 


I 1 


1 1 


1 1 


1 



( 



Fio. 3. Characteristic curve of Brush 125-LIght Arc 
Dynamo wltixout Regulator. 



AND MOT0B§. 

maohine wlthant ui; r«aol>tor. Tlie rtadlnsi v*r« ti\ Ukan at tim iDart- 
leupocltlonofcoRimutation. ThJi enrre l> remarkable from tbe fact tbat 
afUir we get over tbe benil, the curre Is almuet perpeDKcular, and t* prob- 
ably the neareflt approach to a conAtoDt ourreot machlue ever attained. 
By irlndliie more wire on the armaCure the maehlue eonld ha*e bean made 
to deliver a ooiiBtaDt ourreat of ft.O amperea at all loada, wltbout •hoiiUiiff 



bu 


thii 




dbave 






dthelDtemal 




machine 


much 






lent at light 




slat 










e-qiiartsT load 


atfi 


the 


gal 


being 


aim 


»t 


one eleetrioal 



my of the cnirent f ton 

Pie. 4 la a curve at the electrical elDcleDflT. It vlU be notioad that thll 
at full loul reachei H per cent, whloh is accounted for by the liberal allow- 

clrcnlt, and by the large il» of Che vire lued on both Held and airaatBra. 

Fig. fl la a curve of the commercial efficiency. At full load thia la >Tar 
90 per cent, and approaches very cloaely tbe etDclency of Ineandeaeent 
dyiiamoB of equal capacity, but the moat noteworthy point la the high aft- 
cfency phuvrn at one-qaarter load. 

Fix, S la scorve of the machine separately eidted, with DO etureat in tbs 
armature. The ordlnataa are the volla at the armature larmlnala. and tha 
alwclstir the ampereg In the field. Thli la Id reality a pemeablllly OBTre ot 
the magnatlo circuit. By a comparison ol the tollage ihimMn iriun 



DTlfAMO GHARAGTEBISTICS. 



339 



1 



tbere ve Bine amperes in the Held, with that of the machine when dellTer- 
faig eamnt, can be seen the enormous armature reaction. The onrTe also 



















■ 


^ 


"^ 














mo 














X 


r^ 


























^ 


^ 






















MOO 








> 


/^ 






























r 
































/ 




























moo 






/ 
































j 






























NOO 




T 






























1 




"t 
































f 


























































■ 


4000 




































































•000 


































tooo 


















E.M.P. 
















































• 






























BlOO 


































BOO 
1 




































1 1 


1 1 


i 


k ( 


i ( 


1 


r 


1 { 


1 


A 1 


1 1 


1 1 


t 1 


4 1 


% 



Fig. 6. Permeability Gurre <rf Magnetic Oironit 
of Brush 125-Li£ht Arc Dynamo. 

indicates a new departure in arc dynamo design, namely, that the mMnetio 
ciremt is not worked at nearly as high a point of saturation as in the old 
tjpes. 

Skmt dynamo. Tlie shunt dynamo has, besides an external characteritHc, 
■bovn below, an internal characterisHo. The first is developed from the 
Tolii read while the load in amperes is being added, the armature reyolu- 
Uons being kept constant (See Ing. 7.) 

Adding load to a shunt dynamo means simply reducing the resistance of 
tbe external circuit. With all shunt machines there is a. point of external 
mistsnce, as at n, beyond which, if the resistance is further reduced, the 
Tolts will drop away abruptly, and finally reach zero at a short circuit. 



,.-' 



}n 





i 



Miftwe T^Km m f leto 



b 

Fig. 8. Internal Charaoter> 
istio of Shunt Dynamo. 



^10. 7. External Characteristic 
of Shunt-wound Dynamo. 

The internal ehairaeterisHe^ Fig. 8, or, more correctly, curve of magnetiza- 
tion, of a shunt dynamo, is plotted on the same scale as those previously 
deoeribed, from the volts at the field terminals and the amperes flowing in 
ttie fleUtwinding. 



DYNAUOS AND MOTORS. 



Til* nditanea Ui 



a to tlia potnt a on tba onrre. ukd tb 



leo aonlj kppllea t- . — r— - _ — 

__„ b lot (bat polac ia detsnnliiail bjohnu law, or ■■ fat 

lows : Am the aurre oE magDetiiatloD Ig dctermliiea from tbo rakdln^ of 
nlto plotted Tcrtlckllj ksd ampeiei hoiliantall j, and m r = y or r = ^-i 



1 -—i^Uiagaob, therafors the resljtuMs M kny point on UucnrroTlD 

u'of the 
obtaload 

i«of aoB- 

■tdenble importuioe vhore mora tluB 
one drnuno la to be B>nneet«d to tlw 
Mune olronit, or when close reKnlalliia 

Fig. II la a Eunple oorre from m oamt- 
ponnd-woond dynamo, where the ia- 
oreue of munetlzatfon of the tlddi 
dae to the leris oolla and load oaniM 
tbeCecmlnalToltaeetoilMaathelaHl 
)■ Inorsaaed. Tbla la commonly dOM 
" ke DP for drop In feeden to Of 

,r,Buaa 1 of dlsCrlbaUon. It la Imptal- 

' ble In ord[nar7 oommerolal drnanua 

to make thla enrre oloael; approach ■ atralght line, aod the antfior baa 
tODDd It dllBcalt tor good makea to approaoh a alralght line of regoiatlia 
nearer than It per cent elthar aide of it for the extrame rarlatlon. 

Ctarre vr MacHiIM IMalrlkatl**. — This ourre la oonatmctad 
from ailatlng djnamoa to show the dlatrlbntlou of (he Held aboni the pola- 

K'neee; II can be platted on (heregolai rectangular eo-ordinate plan, or oa 
epolar co-ordinate. 

The foUowingcDt* lUnatrate the commoneat mathoda of settins the data 
for the onrre. Wltb the djmamo ranalng at the ipeed and load dealr«d, (he 



pilot broah, a, in Tig. 10, or the 
la started at the brnah x. and 'morlng 
the difference In Tolte between the ' 
bruah, a, la read on the Toltmeter. 




ARMATURES. 341 



Dtreet-enrreiit armatnres are diylded lato two ffeneral f onus. — drwit arm«- 
toxea. In whieh the condnctors are placed whoUy on the snrtaoe or ends of 
a ejlindrlcal core of iron ; and ring armatures, In which the condnetors are 
wofuid on an iron core of ring form, the eonductors helng wound on the out* 
side of the ring and threaded through its Interior. 

Another form need somewhat abroad is the disk armature, in which the 
eoBdnetors are arranged in disk form, the plane of which Is perpendicular to 
the shaft, and without iron core, as the disk rerolves In a narrow slot be- 
tween the pole-pieoes. 

Annatnres of the slotted or toothed core type are almost exolusirely em- 
ployed now. The coils are set into the slots, with the results that eddy cur- 
rents In the conductors are prevented and the conductors are positlrely 
driTsn hy the core teeth. The cores are built up of sheet steel disks in small 
siMs, annnlar sheets in medium sises, and staggered circular segments la 
largi slaea ; the steel Is from 16 to 2S mils thick and the sheets are clamped 
firmly together by end-plates. In order to prevent eddy currents in the 
core, the dlaka or sheets are either coated with an insulating varnish or 
separated by tissue paper pasted over the entire surface of one side of each 
disk or sheet. 

The toothed armature has the following advantages and disadvantages as 
compared with the smooth body: 



1. The reluctance of air-gap Is minimum. 

2. The conductors are protected from injury. 

S. The conductors cannot slip along the core hy action of ^e electrody- 
aaBiie force. 

i. Eddy eurreats in the conductors are almost entirely obviated. 

6b If the teeth are practically saturated by the field magnetism, they 
oppose the shifting of the lines by armature reaction. 



I. More expensive. 

S. The teetn tend to generate eddy currents in the pole-pieoes. 

3. Seif-induetion of toe armature is increased. 

If the slots can be made less in width than twice the air-gap, so that the 
Ifaies spread and become nearly uniform over the pole-faces, but little 
sffeet will be felt from eddy currents Induced In the pole-faces. When It is 
not poasible to make such narrow slots, pole-pieces must be laminated in 
the same plane as the disks of the armature core, or the gap must be eon- 
ridcrably uicreased. 

n^BteruiM In the armature core can he avoided to a great extent by using 
the Dest soft sheet iron or mild steel, which must be annealed to the softest 
point by heating to a red heat and cooling very slowly. Disks are always 
poneheo, and are somewhat hardened In the process; annealing will 
entirrty remove the hardness, and any burrs that may have been raised. 

Disks should be punched to sixe so carefully as to need no filing or truelng 
19 after being assembled. Turning down the surface of a smooth-body 
snnatnre core burrs the disks together, and is apt to cause dangerous 
1*****^ in the core when finished. Light filing is all that i8 permissible for 
truing vp aueh a surface. Slotted cores should be filed as little as possible, 
and can aometlmea be driven true with a suitable mandrel. 

Armiatmre ahaftt must be very strong and stitT, to avoid trouble from the 
nngBetie pull anonld the core be out of center. They are made of machin- 
ery steel,_aDd have shoulders to prevent too much endwise play. 

* X o 



Cmrm Timsil«tln« — A great variety of material is used for insulating 
tke eore, inelndlng asbestos, which Is usually put next to the core to prevent 
damage from heanng of that part, oiled or varnished paper, linen, and silk ; 
praasDoard ; mica and micanite. For the slots of slotted cores the insula- 
tion ia frequently made Into tubes that will slide Into the slots, and the con- 
ductors are then threaded through. Special care must be taken at corners 
and at turns, for the Insulation is often cut at such points. 



DYNAMOS AMD MOTOHS. 



For kU Hull dTnainiia, ud In muijr of conildanbis gin, tbe wiadlDf ta 
of doubla eatton-covared wire. Where tbe required oarryiug upuliy |« ' 
more Ibui thai of a Ho. 8 wire, B. & 8. gauge, the conductor inould b* 
itruided for amootli-core arniatures. In liirge djoiuDaa, reotaugnlar cofB { 
per bAn, oablea of twiAted copper, uid lanomeouefl luve cehU comprcMAd : 
Into leoMngulM shape, are more camntoDlr lued. If the capper ban »« ' 
too wide, or wide enouEh eo that one edge uf the bar enten the fleld p er ea p 
tlbly before tbe ramaiDUig parts of tbe 5sr, eddy currenti are Indneed la li ; : 
■uch ban a» therefore made quite narrow, and It I* common to alope the - 
pole-faoa a trifle, ao that tbe ban may enter tbe field gradually. 

iItlhod$ or armngatttiu of v!indimii ate ol a moit oomplai nature, and 
only theiDOet feueral [n u» will be daacrlbed bare, and theM only tn tbeorr ; 
Panhall £ Uohart bar* dtHcrlbed aboat all tbe poaelble oombinatluoa ; 
8. P. Tlioiii|iaoa,Uawkiua£Wallli,BudoCbare bare alio written quite fallT 
on the iDbleot. 



There are two fundamental types of armature winding : ring and dr 
In a ring-wound armature, the core !■ nereuarlly anaular, tbe wire b> 
wound tbrough the core as wall as along tbe eitarior, as Indicated In f 
13 to is. This form of winding la now used only In aro-llghl dynamos 

The llmpleet form of ring wlndluB [s the tvo-<:ir«ii( ilapir windiiu, wl 
a conllnuoua conductor Is wound about the ring, and taps taken off to 
*""■"""*•*- %t regular Interrals. 



n this will be the mHJM-cirruil tingle wind ia^, d 



-«.: 



circuit winding can be crou- 
occuPTlog ilmllar poelllons ! 
the lame commutator bar. I 



number of commutator legmen 



lo awib Mgmant luil«ad o: 



Die aiuiit>ar of pol«, 



Bat twOHti oibnubM uauvxtimij for Iha twoflrcnJC vlnilliin. anl 
Ha corrflnt 1« hesTj «ioiu[h to rsqaire ■ long comicatator. In tEIoI) ci 
dUmt Mta Df btnthea eta be added, up to tha noinlMC of pole*. 



. mug WtivUns Croae-oonnected Co Bedaoe Uucqnol Indastlon, 
lecllon type of this olut. oonduatora under sdjaeeDt Held 



i 



>ol« KTeeoDitMitod togetiieVio' that tbecirculu froia broah (o briuh are M 

InJIanioed bj allthe^le* itnd^are tbereforaequal. __ .^ , H 



lonioed b j all the pole* and . 
[b the faN-rowuwnDii tfpe th 
rted, mt that the coDdnclon 



ii<n!t«, ■<• liuai me coDdnclon from bruah to briuh are Inauenoei 
oaeiail the number of polee. 
Tlie number of Mill Ina rvD-eimiif long-eotaiection tmtU^olar lei 
■- d b; tbe lonnala 



i 



bar of paiTM of polea. 

nie pitalk, y, u the namb 
for Inatancet ui an armatni 



,ber of colli adra 



i. the b^nnlEK otcoirF+ 

i„gtoi 

.. _ ._ iflngta 

tana* between broabea for tbli olasi 



^ItlpolMrtfiptong-connecHon wi „ , , . „ 

Kapp glvea In the folloiAnE table the beat practise sa to uignlar dli- 



DTNAU08 AND UOTORS. 



•>t™l«. 




AnBul«dl.tanoBbetw«i. 


bnuhoi. 






.Degreen. 


Degree.. 


D.gr«,. 


D.«««l. 


D«CTM.. 


2 


180 










« 


«0 










< 


60 


ISO 








B 


K 


IX 








10 


36 


106 


160 






W 


30 


90 


IW 






14 


».T 


77 


US 


160 




le 


2i£ 


ei£ 


111 


IH 




18 




to 


100 


IW 


160 


ao 




« 


M 


136 


Iffi 



^ 



Fig. 17 anoUier mapk u naed wIUi ■ gTeftt«r number ol pt 



Fio. le. TuD-path Uultlpalir WinJlngx. Fia. IT. 

Both ol the nbDve eunplea are of the Irmg-ctmntcliint lypa- In the it 
(wniucfion type the fonunU for determining the Dumber of the eoU la 

and Fig. 16 ia • Muaple diagram of thli Ijpe. 



ARUATURES. 



Pio. 18. BhDrl-40Dneet[on Tiro-pntli King Winding. 



tn order tluU th« E.IiI.F.'i gsneuteil In the coUii of ft drum knnatan lattj 
teln UM*une dInBllon. ttli neCHHur Itmt thet*D sldiH of «uh coll be la 

* -■ desof the..::. 

II bipolar maoMiua, and part 



li of oppoalte poUtitT. and thsretora the aides of theooilaaieoonDected 
— ---^-^Tonheflore; direc '— ' ■-' — "' ' 



d[ the multipolar type. 



no, 19, Bipolar Dram Winding. 

Tbe dnua vlnding la wholly on the exterior of the sore, FIb. 19 Is a dln- 
■rain of a bipolar dram vlBdWopa nuoolh core ; the dolled Imce Indicate 
IhecroHing* of the Tiros orer the rear head of the core. Dram windings 
are moatlT of the tvo-lajer type, of whieh P^g. 10 J« a dlaarua; wltli a 
(btted core, the oumbered conifac tors would lie within thesloti. In this 
diagram eacfa pair of condaclors harlng niimbcn dilferlng br IScompoge 
the twi>"(ldas" of one coll, and are therefore Integral with eashotbet. 



DYNAMOS AND MOTORS. 



nsrnl tTpea of drum wlndinjE; Up fti 

s dlitlu|[QfBblDg tensB. Blpolu- machlue* ueoenkillr 



FlQ. 20. Jllpolar twu-liiyer druni wlodluc. 






Flo. II. Two-pnth single fonr-pols winding 

baTelap-soDiiBctedirliidliigg. In mal tl polar mnobl nee the two "alda" of 
eiwh coll tn liwuted n dlstsnce snart approilmiuelv eqatl u> the pal* 
pUph Initsad of on oppoKite sides of the core (lee Fig". 21). TUa proporSeo 
of ■rmatnre olreomlereDcs apanned bjr eai^ coil li preferkbly > trifle 1<m 



ARMATOSES. 

tkan the pals nltoli ; for > toothed amutim t&a nmnbar of taatb 
by <ach ODil ■Eould be egnal Ui A'l — p ~ xi . llA', — p\t% whole . 
zi = li l( U Is ■ mlied!^iiumber.:n = thelTMUoaKl putorl + th 
U ihoDld aeldom SMeed 2 in ui j sua. 

Alllap vlndioa have Jt m parallel paths. A multiple' vritLdlbg 
of (vo or more dutlDct vlndiD^f the couducton of wlilch are am 

tt eaaunntator aegmeuta aHembled In a amgle comiautatc 



Wm. SZ. Bii-path alnile 



ITJJ. J3. 



_ I 

tiare an; eren number of narallel patha ^ 

net polei. within practicaJ limits. The ■ 

if aafle and method of connecting thorn. W 

>f onlle (and commnlacor segmcnli^, noni. \ 



The nikllar Talne of >■ la preferable, bat choice betwMn the two la tun- 

■ ally detennlned by the oholie between the r--'" ' • -'-■••— " 

■■ + 1 and m haTB a common f«ct.>r. the w 
I aoiUp'--- ■•-- - -■-- ' 



detenulued by the choice between the reHultlng cljuseaof w 
.■ 1 and m haTB a common f«ct.>r. iho winding will be of tho 
inldplei tn>e ; If not. a aimpla waTe-eonneoMd winding will It 



In slotted armatoree the niunh«r of conductors must be a multiple of the 






DYNAHOS AND MOTORS. 



ng. IS !■ k dlasrsm ot & two-pUh trtplsi winding, i^., thrM tvo-pal 
IndtDg* HDUMted In piirallel br the briubsg. II b mathenuUcitllT U 
IhItbIsdI of k alHgls ■Ii-pBth winding. 



-hiSti 



Fig. M (hmn dl>c'*''i<'»tl<'*llT tl'> chanoterUtla ot the oaiul tw»«al 

Mure wlDdliig died on itreet rallwsy motor*, In which there mra thn 

■ M muij eoUa M there ue alote. In thi* oHe n = 0.3S Ukd fa = " 



ARMATURES. 349 



tmm mmtrmmtU GIvcvite im H^ymmammB. 



IMfBenltT htm been experienced in the operation of Urge multipolar direct- 
nrrent mAcblnes with parallel wound armatures, owing to differing mag- 
iBtic itrenfftba in the polee. The potential generated in couduoton under 
At pole differed from that generated in conductors similarly situated under 
■otoerpole of the same polarilT, the result being a slignt difference of 
ptentiai between brushes of similar polarity. This caused currents to flow 
DEcm one brush to another, and from one section of the armature winding 
\» anotheTjattended by wasteful heating of conductors and sparking at the 
This difficulty is obviated by the Westinghouse Electric s Manih 




betwing Companv by the following method of balancing : 

A nnznber of points in the armature winding corresponding to the num- 

Wr of pairs of poles', which are normally of equal potential, are connected 

W leads through which currents may pass from one section to the others 

vtth wliich it IS connected in Darallel. The currents are alternating in 

cksmrter and lead or lag with reference to their respective EJd J'.'s. 

r thus magnetize or demagnetize the field maimets and automatically 

[see the necessary balance. This method of balancing is also of advan- 

Ib eliminating the sparking at the brushes and the wasteful heating. 

ik occur when an armature becomes decentralised, owing to wear ox 

tte bearings, or to other causes. When an armature gets out of center the 

air-g>p on one side is greater than the air-oap on the opposite side. The 

fdoitlal generated in the coils — if the anuMure has the ordinary multiple 

winding— will be much sreater on the side haying the smaller air-gap than 

that generated under poles of the same polarity on the opposite side. Con- 

isqaently . a current correspondinff to this difference of potential flows 

fhmigh the brushes from one section of the winding to another. This flow 

of eurrent will act the same as if two generators were coupled rigidly on one 

■kaft and the poteutial of the one raised above that of the other. The 

Bsehiae lunring the higher potential would act as a generator, and the 

otksr would run as a motor. This, of course, would result in bad sparking 

and the burning of the brushes. 

Bj the use oCthe above balancing method, however, the armature could 
ke considerably out of center and no injurious results occur, as the balano- 
isg ettrrents flow, not through the brushes, but, as explained above, through 
9«d*Ily provided connections. In addition, the currents in these conduc- 
tonare alternating currents—'* leading" in some coils and ** lagging" in 
othen— a fact which enables a relatlveqr small current to balance the oir- 
eoitifffectlvely. 

The temperature an armature will attain during a long run depends on 
Hi peripheitd speed, the means adopted for ventilation, the heating of the 
Mnductors by eddy currents, the heating of the iron core by hysteresis and 
sddr currents, the ratio of the diameter of the insulated conductor to that 
of its copper core, the current density in the conductor, the radial depth of 
vioding, whether the armature is of cylinder or drum type, and the amount 
asd ebaracter of the cooling surface of the wound armature. 

The higher the peripheral speed of the armature the less is the rise of 
temperature In it. Mr. Esson gives, as the result of some experiments on 
iZBiatures with smooth cooling surfaces, the following approximate rule : 



iSr(l + 0^)0018 V) "" «S'( 1 + 0.00060 K') ' 

vkeref^ := difference of temperature between the hottest part of the arma* 

tore and the surrounding air in degrees, Centigrade, 
Pj^ = watts wasted in armature, 

5 = active cooling surface in square inches, 

jy =: active cooling surface in square centimeters, 

V = peripheral speed of armature in feet per minutei 

V = peripheral speed in meters per minute. 



r 



350 DYNAMOS AND MOTORS. 

The more ef&cient the means adopted for ventilatlnff the amuitiiTe ■ 
cnrrentB of air, the smaller is the temperature rise. Some makers lad 
spaces between the winding at intenrals, thos allowins the air free mm 
to the core and between the condnotors. A draught of air through tbe^ 
terior of the armatwe assists cooling and should oe arranged for wlie 
possible. 

For heavy currents it is sometimes necessary to subdiTide the oondi.. 
to prevent eddy currents; stranded conductors, rolled or pressed hydrai 
ally, of rectangular or wedge-shaped section, have been used. Such 
division shoula be parallel to the axis of the conductor, and prefei. 
eifected by the use of stranded wires rather than laminie. Few armat 
conductors of American dynamos of to-day are divided or laminated fni 
degree whatsoever. Solid copper bars of approximately reotangalar eiu, 
section are often used, and little trouble is found from FOucault oarrenlfc^ 

Mr. Kapp considers 1.6 square inches (9.7 square centimeters) of c< 
surface per watt wasted in the armature a fair allowance. 

Esson gives the following for armatures revolving at 3000 feet per mini 

P^ = watts wasted in heat in winding and core, J 

S = cooling surface, exterior. Interior, and ends, in square innhij 

S' = cooling surface, exterior, interior, and ends, in square oeflij 

meters, ^ 

^^ = temperature diiferenoe between hottest part of armatareMl 

surrounding air in C^. 

Then 0^^±^ or ^t^. 

S ^ 

Speclfloatipns for standard electrical apparatus for XT. S. Navy sav. "St 
part of the dynamo, field, or armature windings shall heat more than 60° M^ 
above the temperature of the surrounding air after a run of four honnsi 
maximum rated output." -««*• -» 

According to the British Admiralty specification for dynamoe the tear 
perature of the armature one minute after stopping, after a six hours* rS, 
must not exceed 30° F. above that of the atmosphere. In this test the thZ 
mometer is raised to a temperature of ac F. above that of the atmosphsn 
before it is placed in contact with the armature, and the dynamo oomnlifli 
(or does not comply) with the specification according as the thermomei« 
does not (or does) indicate a further rise of temperature ^^^^^^^ 

The best dynamo makers to-day specify 40^ and 46° 6. as the maximum 
rise in temperature of the hottest part of a dynamo, or BS® If the t«mi>em> 
ture of the commutator surface is to be measured. 

In many direct-current dynamoe having no special devices for rereraiJig 
the current in each armature coil as It passes through the " commntaHS 
■^5i®» li' *■ necessary to rive the brushes a forward lead so that the raj? 
nettc fringe from the po^tip toward which the coil is moving may induce 
*?ir'?-^* *" ^°? *^" *°^ reverse the current. In motors thebrushee si» 
shifted rearward instead .of forward, the polarity of the approaehlns sole' 
tipbeinff of the wrong sign. * *^ 

With the forward lead Sven to the brushes the effect of the armature eu^ 
rent is to weaken and distort the magnetic field set up by the field m^g. 
nets ; a certain number .- depending on the lead of the brushes— of thesr* 
mature ampere-turns directly oppose those on the field-magnets and rendsr 
a somewhat larger number of these ineffective, except as regards waatltf 
power ; the remaining armature ampere-turns tend to set up a magnetic fleM 
at right angles to the main field, with the result that the resvdtant fleM 
Is rotated forward in the direction of motion of the armature, and that ths 
field strength is reduced in the neighborhood of every trailing pole-pieoe 
horn, and is increased in that of every leading pole-piece bom. When, 
therefore, the brushes have a forward lead each armature section as It oomef 
under a brush enters a part of the field of which the strength is reduced bf 



DraECrr-CtTRKENT UOTORS. 



353 



^ 



i = 



(LordKelYin.) 
andP = 



vlwre 






If =r moment of couple on axis, 
Pz= preesure on eftcn bearing, 
W = veiffht of armatore, 
k ^ nuiiui) of gyration about axis, 

Sir 
0=? ^ w4 = maTimnm angular velocity of dynamo in radians per 

■eeond due to rolling of ship, 

A = — =: amplitude in radians per second, 

(Radian is unit angle In circular measure.) 

d =r degrees of roll from mean position, 
T rr periodie time in seconds, 

M = 2 m = anffular velocity of armature In radians per second, 
n = number of revoUitionil of armature per second, 
i = distance between bearings, 
g = acceleration, due to gravity. 

Note. — On applying the above formula to dynamos, where IT, k, aii<^«D 
sre great, it will be f aqnd advisable to place their plane of rotation athwart- 
ihips, in order to avoid as for as possible wear and tear of bearings due to 
t^ gyrostatio action. 

The eounter B.M.F. generated in a motor armature is given by equation 
(1). This E.M.F. is equal to the E.M.F. applied at the motor brushes minus 
the drop in the armature winding and connections ; consequently, the speed 
of a motor la 

B.t>.m. = '»<^ ''-^-")^'» (4) 

At no load, the drop in the armature circuit is so small that Sw — ImR 
my be eooaidered equal to £«, for the purpose of computing the no-load 



(6) 



The torque of a motor armature, in pound-feet, is 

r=ii7*^«f-pi<r" . . . 

Motors for operation on constant-potential circuits are : 

Shunt-wound, for service requirfiig practically constant speed and im- 
poses small load at starting ; 

Senes-woond, for starting heavy loads from standstill and running at 
apeeds inreraely varying as the loftd ; 

Compound-wound, for starting heavy loads and 
numtag at nearly constant speed. 

Differentially-wonnd, for starting under light 
mads and running at strictly constant speed. 
(This type la not mneh used now.) 

The remarks concerning dynamo maffnets, ar- 
iMtareB,ete., apply also to direct-current motors. 
The magnetiaatlon curve may be obtained by drfv- 
mg the machine as a dynamo ; or it may be plotted 
iFom readings of field excitation and armature 
Bpsed ; in the latter ease, the curve will be the In- 
▼ene of Fig. 1, as indicated by Fig. 25. 

Brushes on a motor muRt usually be Set hack of 
rae neutral point, or with a ** backward lead." 
TUs tends to demagnetize the fields, and as weak- 
Ming the fields of a motor tends to increase the 
^•ed, the increase of load on a shunt-wound 

>K>tor tends to prevent the speed falling, and the shunt motor is very 
Asarly self-regalating. 




i 



Fio. 25. Magnetization 
Carve of Motor. 



DTKAUOa AND UOTORS. 



I con^enble 



H. Ward LMDud Inveuted tbe method bLuwu 
mo«t Biaallant mnlti, Klchough to some eiieat en, 
•fllolaDt. 

Tba drlTliig motor, or ntbar motor wlilali It li viBhsd to oontnd, la p 
Ttded vlth a Mpuately aiclled flald, vblob sMi b« TBiied bj IM rfaeottM ^ 
prodace an; rata of apeed, from just turnlnc to the full ipeed of irhleh % 
mar ba c*pabla. Corrent Is supplied to lla Knuatun from a s«pankt« f ~ 

enlor, aud bj tujIdk the aaparatel]' exalted fleJd of thlasenari ' 

amoont of eucreot lapplled to the motor armature can be Taried at 
the torque Eherefore cbangsd to suit Ch* clTsumitanoei. 

Thegsnerator is driien at ooDatant nwed bj direct ea — 



which get) lt« c 




Fig. 26. Leonard's Sntem of Hotoi 



BtfoT'" 



entoraoppllM ODirent for i 

Bt rerenliu tba flald of the earn 

reversed, andlfaerefoTe so is the direc 

Fig, 27 showi the Leooaid BTstem ai 



Tkrwe-irir* SjiMBa far Tarlab 

OmlttlBf sraaes, street rallwajB, holiits, and otJier i 



{I) Machines requiring . . 
fans belong to this class. Tbe poi 
v»rj rapldfj -- "■ •" '-— 



Taiiabla apM 
GTMalng Kith tbe spaed. Bloi 



w the speed iBcreaset, i 
UDh eervlae. However. 



<2) Machines 
Is usnall; Binml' 



IDUed for ^e machine J 

bould be axaroised In seteeuDf 
rarlatlob required Is usoaln 
idard motors od a single nt ' 
„„„.j jfl nomiHiund-if Dund aud tb ~ * 

The speed variation n 



■eterably b. 



id aud the apeed 



d blo' 



equlred for such aervlea 

of tba shant fleld tEw- 

_.... _HaairlndlnKtBe«peclsllT 

ntlng the heavy fluctuatlona at cvl- 



- oonptant speed motor In > 



PRACTICAL DYNAMO DKSION. 



355 



rk beeawe « eoaatant speed ftt any point on the controller !■ not 

{^ Machines requiring approximately the saoie maximum output at any 
iMd, or a torque yarylng liiTersely as the speed. This class includes most 
tthe machine tool work where automatloauT constant speed regulation on 
notch of the controller is especially desirable. It is, therefore, neces- 
ta> ose a shunt motor haring good inherent regulation. 

C>««enit«r.— The stanoard Edison three-wire system for general 

ition consists of two 12(>volt generators connected in series with 

I awtral wire brought out from between them. A single generator of the 

rell Toltage, with a motor-generator set of sufficient capacity to carry 

I BBbslanced current, is used in many places. Still another system con- 

I tecsdlT of a standard direct-current 

ntor designed for the maximum 

fSfoind EJi.Pr having collector rings 

•osseeted to the armature windinc lile 

atVMhsM rotary converter. Theleads 

ftsnttese rings are connected to auto- 

tmrfarmers or balancing coils, the 

■iddle points of which are connected 

to tiw Beatral wire. With no external 

i^erieM whatever, the neutral wire is 

i ttu maintained at a voltage midway 

! tstvtea the outside wires of the system 

|M» Jig: 28). These generators may be 



1 9*nted in multiple with any standard 
! Itne>vire i 



system, whether it consists 
«tyo machines operated in series, a 
■BfleToltsgeceneratorwith a balanc- 
iig wt or a double commutator gen- 
mtor. Any standard single-voltage 

ijitimmay be changed into a three-wire system by adding collector rings 
to tk« generator ana using balancing coils to supply the neutral wire. 




Pm ACETIC AX. lOmtAMO l»KSI«ir.« 



It li nis to follow the rule of using bipolar fleld-magnets for maehlnes of 
lulovttts or less and multipolar magnets for larger machines. 

For eommatation reasons the current passing anv one set of brushes 
Mould oot exceed 260 amperes ; this gives a criteiion of the number of 

Cka for maehlnes of 260 amperes output or more. Lap windings should 
ved on such machines. Then 



1» = 



0. 006 Tm 
m 



(«) 



The nomber of poles on machines having wave-connected armatures is 
wemlned by commutation considerations oniefly ; more than six poles are 
Mdomnsed. 

The best construction Is a laminated magnet pole with extensions at the 
w-gap end. bolted to a cast-steel yoke. I^rly good results are obtained, 
jl^ever, with cast-steel poles. Laminated cores, cast-welded into either 
ina or steel yoke and provided with cast-iron shoes embracing the ends at 
tte sir-cap, give excellent results if the east^welding is properly done. 
^fom the ratio of air-gap length to the width of each armature core-slot 
^^P^niag is maeh less than 0J(, the pole-face should be laminated in order to 
Vvftn excessive eddy curents in it : otherwise it may be solid. A cast-iron 
poleehoe must not cover the end of the magnet core, but should surrotind 
n ud serve merely as lateral extensions ; the cross section of the core 
■hould be slightly reduced where it is surrounded by the pole-shoe. 

• Cecil P. Poole. 



i 



356 DYNAMOS AND MOTOB8. 

The E.M .F. generated in the direct-oorrent armaiare ia, from eq. ^), 

P q W 

which reduces to 

B = 0.06236 IhWp^Bf-^' ■'•pm. VT* -^ q. 

The output In vatta is Pw = E» /«, which for preliminary puiposas 
be considered the equal toEuq; whence 

P« =0.06236 ZV FF>V' Bp««'^« r-P>ui- 10-* ....<! 

For eooaomioal use of material, the projected outline of a pole-f ae« alioiH 
be square, so that the width parallel to the armature shaft should appatin 
matel; equal the chord of the average polar are: whence Wp shoaM 
be= Z>^ dn (180 V* -r P)- For moderately high-apeed maohinea, ^ mmj bi| 
Uken at 0.7 ; for slightly lower speeds, at 0.72, and for slow-speed nuielkliM^ 
at 0.75. For reversing motors it ia beat put at 0.6606, except aeries-wouaa 
reversing motors ; finr ^ese, let ^ == 0.7. 

Representing sin (180 1^ -ri?) by li^, page 371, results. 

The average magnetic density over the pole-face ranges from 25/Mn t^^ 
60,000 lines per square inch, according to the designer's method and the 
of the macmne. It is rational to make B^=c x Dp^^yO being aeoeffiei 
varving according to the type of machine. For constant^tential drnai 
and motors for general service, 28,120 is a suitable value for c ; for annnt 
compound-wound reversing motors, 33^60 is appropriate, and for rnvries t9^ 
versing motors, 36,620. 

The permissible number of ampere-conductors around the armature paifr 
phery ranges from 1200 to 2200 per inch of armature diameter. For 
chinos designed according to the method outlined herein, it la 
practice to apply the formula: 

The values of kt are as follows : 

Dynamos and motors for general service, ka = 679. 
Shunt and compound reversing motors, ke = 564. 

Series-wound reversing motors, ke = 678. 

From the foregoing equation an equivalent Is obviously obtainable for 
UHe ^, and substTtutmg tliis and the equivalents for Bp ^nd Wp prerioaaly 
obtained, equation (7) reduces to the following two : 

For all machines except series-wound reversing motors : 

„ tA/>p*-*r.p.m. ^ 

^-=—100 « 

For seriea-wound reversing motors : 

i>» = 0.013 Au 1V> r.p.m (^ 

For belted machines which need not have any particular rate of speed, as 
economical rate is 

8500 
r-P.m. = jy;^' 

Considering Dm and Dp equal, which is allowable in preliminary " rough- 
ing out," ana substituting in equation (8) the above equivalent for r.p.m.: 

P. = 85 JtM A>*'" W 

Araaataire Iletaila. — Gore disks 25 mils thick mav be used in moat 
armatures ; only those In which the core is subjected to nigh rates of 
netic reversal need have thinner disks. When p x r.p.m. exceeds 3000, it 
advisable to use disks 20 mils thick, or less ; wnenp X r.p.m. exceeds 4000, 
15 mils should be the limiting thickness. The final criterion, however, li 
the eddy current loss in the core and teeth. 



PRACTICAL DTNAUO DB8ION. 



367 



I HaTlng a means of determining the pole-f aoe width parallel to the arma- 
twe abitft, the length of the armature oore follows within dose limits. 
Ihe armature oore ahoold extend beyond the edges of the pole-face at eaoh 
tad by a smaU amoont^not less than the aix^ap length, and preferably 
15 times the air-gap. 
Armatnre cores more than 6 inches long should haTe Tentilatlng duets 

■ot ksB than | inch wide at interrals of 2# to 8^ inches. The exact duct 
I vidth is usually determined by the amount of steel required paridlel to the 

•luf t in order to keep the magnetic density in the teeUi within suitable 

Umits. 
The" nominal " magnetic density at the narrowest part of the teeth should 

be between 140,000 and 165.000 lines per square inch of net cross section. 

The "nominal *' densitr is that which would exist if the flux did not spread 

bsjond the geometrioai contour of the pole-face In passing from the latter 

l»tks armatore, and if all of the flux passed through the teeth ; that is, 

,- ,^ — = nominal density at tooth roots, 
wa = 0J» ( IT* — yentiUting ducts). 

Is Older to obtain dimensions that will result in a ** nominal " density at 
tbe roots of the teeUk that will be within the specified range, the number of 
teMh (sad slots) may be approximated by means of the formula 



wDt- 



At = 



Vfm 



(11) 



Themmber of teeth must, of course, be an Integer ; If the result of eq. (11) 
■booU be a mixed number, therefore, the fractional part should be discaraed 
U it ii 0^ or lees ; if it be more than 0.8, the next higher integer Is to be 
taken as the number of teeth. The net measurement of the armature iron 
psnliei with the shaft must then be corrected to satisfy the equation. 



«^ = 



ki 



Us value of Ai for all oases is 



9D*^9lf$ 



(U) 



When the armatore eonduetors are round wires, the size of the coil slot 
if determined chiefly by thesise and arrangement of the wires. Form-wound 





% 



W^ 



J 



Fie. ao. 




^ 



uid Mparately-insnlated ooOs are generally used, so that the coil slot is 
^ uY?^^ of one of the shapes shown In Fig. 29. the slots a or ft being used 
l^eubliidlnfF wires are employed to keep the wires in their slots, and one of 
•*• others Trtien the colls are held in by wedges. Two-layer windings are 
2™Jost iarariablT used in this country. Fig. 30 shows two half-coils 
araesst" in eaoh layer, each coil haying three turns of wire ; this makes 



358 DYNAMOS AND MOTORS. ' 

the toMl QuDibtr of soils twice tba nunibar of ilota. Tig. 31 alioiri UuM 
half floila " nefllwl." witb two turrti p«Tcolt ; thfaglrfle thi^ llnrn a« vumf 
eolliu (bare are Blots, "tliraeeoUe per slot." iirBaitremelTobtwittoiiiilA 
to '■ neat " the eoile, but MmetimeB unaToLdsble when round wirw lue iwei. 
Table II, p. 372. glvei elot widche and deptlu suitable for rarions Brran|» 
mania ot round eonilur ton dniwn toB. AS. noge, bavsd on two-lnver wtnd- 
ingsuid the tusulatlou Indlnted In Fig. 39. TheindlTldnal ooUa mto tnwfptt 



Fid. SO. Pio. SI. Fig. 32. 

cb ralea-ti 
verlng of 



icb ralea-treated prcM-boud, each trorat el 
Sb oiled tape, h&iriapped, 



and tbe slot !■ lined with a troogb of a,D2-lDah mica-treated preas-board. 

If tbe presB-board Is ■ '■ -•'-■- - - -- 

coils ara dipped and bal 
tlon win be adequate fo 



. .. >t Is lined with a troogb of a,D2-lDah mica-treated press 

If tbe presB-board Is well Tamlsbed wltli Insulatlne corapoimd, a 
ra dipped and baked before being aseembled In the slota, this 



not be less than I of Its depth nor >non 

than i the depth. Tlie depth ot the coil Blot, Cor annatnra ot IS InehM 
diameter or orer. may be eitlmated for prellmlDary pnrpoeee hj meuu at 

•=.+^ „ 

Appropriate trial depths for (he ooil alota at imaUer cores are (tven bf 
Table IILpage 3T1. 

Table iK ^ge 3T3 eIth empirleal bnt pradtlcal trial mines for tlie mini- 
mam allowable numbarof armatore cntln, andTabla V, paf* 874, gives Talne* 
for the mailmnni allowahla number ot turns per coil, for nse In prellmlnatT 

domX eioeeded without riBk of Bparklng at the bnUbea. 

Table VI, page 376, gives trial values for armature oondnclor sins ; the 
actual allowable enrrent density in the conductor!, boverer, la determined 
bT the heating at the armature. 

AFMStBiw Iassvs.— The total losse* In the armature should oc* 
exceed the value which will give a temperaiura rlne 
The relation betveen lont watts, radiating Burl 
and temperature rise Is. tor talrly well ventilated ai 
Held magnet trames, approilmately u lollows : 



peripheral velodlT 
ires in ni>ik.«DOlOHa 



and allowing a riae ot 7D° this ( 



O.IF.fl- 



PRACTICAL DYNAMO DESIGN. 359 

The roMoo for laklng P*^ insteMl of Pj^ m the eritarion of heftHag to 

tbftt the projaetlng parts of the winding do not act effeetively in radiating 
0M \%!emX produced by the core and teeth loasee, although their radiating 
■■rf ace ia always ample for the iV ices In them. Since they are not included 
in the radiating surface, the loss in them is not included in considering the 



With round conductors, the watts lost in the embedded part of the wind- 
li^ will be, with sufficient accuracy, 

if the condootors are rectangular In cross section, -z — must be substituted 

for ^ in this equatioA. 

Tlie kMsas in the armature teeth must be estimated separately from those 
in the body of the core, the densities being widely different in the two parts. 
The general formula for hysteresis loss in either part of the core to 

Pk:^4IMchvp r.p.m. 10" » 

and the formula for eddy current loss to 

P« =r 4 ktvp^ (r.p.m.)« 10~« 

fai which kk to the loss per cubic foot of iron due to hysteresis, as giren in 
the table on page 100 and k* the corresponding eddy current loss as gireu in 
the table on page 100. It should be borne in mind that although uie con- 
ftanto taken from the tables mentioned are based on losses per cubic foot of 
iiOB or steel, the Tolume of iron or steel represented by v in the equations 
it fai cubic inches. Combining the three equations Just given, the total low 
ts be considered in estimating the heating of the armature is 

Pa' = FF« a; ^ +P r.p.m. JO"' [48 {vmkk* + vt km) 

-\'OApr,p.m,(vmkm-\-vik0ty] (15) 

In order to allow for the crowding of the magnetic flux toward the slots 
the eroes section of the armature core body may oe taken at 0.8 of the actual 
eross section, making the effective volume 

o« = 0.2 V (ZV — Z)o>) tr« (1^ 

and the effeetlTe density will be, accordingly, 

^=0.8(Z)»-2>o)tr. ^^''^ 

For computing the probable losses in the teeth the following relations may 
be assumed without appreciable error : 



active 
per 



> teeth) /2*^« . ^\« . 
pole }=lr5 + pj^'' 



avenge width of each tooth = (T 4-2 -f 3 ; 

and since (t -f 2 -f 3 = [v (Dm — 1.33 A) — A^« s] -f Nu and the average density 
in the teeth, for the present purpose, is equal to tne flux per pole -7- active 
teeth per pole x average cross section per tooth, the average density will be 

Avg.BT= .2ifc»8 ^\ ' ... (18) 

(^ + 1) [ir(D.-1.3A) + J^i*]w- 

The volume of iron in the teeth to 

WsTj/A.*- j2>i»-A*iVil w. (19) 



PRACTICAL DYNAMO . IXE8IGN. 361 

ihovn vere plotted by Heesra. Eaterleln and Keid from t«8t0 made on a 
ttige number of actual machines. 

In estlmatins before hand the eflElciency of a machine, the loss in the pro- 
Jading parts <H the armature windins must, of course, oe considered. The 
•etuaT total loesee in the armature winding and core will be approximately 

P^*=. UN*^-\-p r.p.m. 10-' [48 {p»hm + wAaw) 

-\-OApx.^.m.{vtk^-\-f)mkmy\ (20) 

In a barrel winding, the length of each conductor ({«) will be practically 
that glTen by the formula 

<• = ir« + Aw (2>« — A) + 0.8 (1 -f A), 

if the oanduoton are bent around |-inoh pins, as indicated in Fig. 35, and 




Flo. 85; 

lAsrvard palled out to span the proper number of teeth. Table Till, page 
3RigiTes raluee of km for different numbers of poles. Each coil will project 
Wjoad the armature core at each end about 

^ <2Jb- A) + ii^ inches, 

sad Ihe distance fit>m center to center of the winding pins must be equal 
to 

W*-\-hm{Dm — h) inches. 



CoMHBstetor aad Br«ali«a.— The number of commutator barss 
santber cf armature coils or elements, in practically all modem windings. 
Tbit diiuueter of the commutator barrel must be kept as small as possible In 
Older to reduce the friction loss at ther brush faces as well as to keep down 
the eoit of the commutator and to fayor good commutation. From purely 
MSfhanica l considerations, 

Dk > 0.06 X Number of segments (21) 

lor Momatatioxi reasons and to keep down friction, 

JDi> 10,000 -hr.p.m (28) 

la flaalty rovndijig out the dlmenoloiui, tiie following relation should be ob- 
Mned, ft possible, 

*=^ <^ 

U|dn I thould preferably be an integer. 

Xbe enrTSDt aensity in each commutator segment should not much exceed 
'''^unperee per square inch in the horizontal part find 2600 amperes per 
*4nare inch in the connecting lugs or risers. 

The brush faces should be of such area and number that the current den- 
fity at the faces will not exceed 40 amperes per square inch for carbon 
broghai, 160 amperee per square inch for woven wire or gause brushes, or 



i 



362 DYNAMOS AND MOTORS. 

900 amperes per square inch for leaf oopper bnuhes. Good areni^ fan 
densities are 90, 120. and 100 amperes per square inch, respectively. 

With pressures of 14 to 2^ lbs. per square inch of brush face, the effective 
resistance of the brushes wiU usually be 
Carbon brushes : 

Copper brushes : 

0.0125 ^ 

M 

The total drop in volts at the brush faces, therefore, will be 
Carbon brusnes : 

^ - volts drop (M) 

Copper brushes : 

— volts drop (3«a) 



90M 



The loss in watts due to the friction of the brush oontaote with the com- 
mutator Is 

M Dk r.p.m. 

H » 

jbt varying aocordlnff to the brush pressure, condition of commutator and 
quality of brush. The total losses at the brush faces, therefore, are 

Carbon brushes : 

Ah Dk r.p.m. ,/•*_„. ^, 

te + 8"^ = ^ W 

Copper brushes : 

Ai Dk r.p.m. J^ _ 

— H — + §r2i=^ ^J 

With ordinarv grades of copper and carbon brushes and a commutator in 
reasonably good condition, 

680 

~ brush pressure in lbs. per sq. inch' 

The maximum efficiency is obtained when the two terras of eqe. (26) and 
(26a} are equal, i. «., when the friction loss equals the P R loss. 
Tne temperature rise of the commutator \nll usually be 

86 X total lost watts ^ ^^ 

= » (26) 



If the lugs of the commutator segments are of considerable length, the 
rise of temperature will be somewhat less than calculated; on the other 
hand, if the commutator and brushes are not in good condition, the loases 
will be considerably more than given by eq. (26) or (25a) and the tempera- 
ture rise win be correspondingly greater. The temperature rise should in 
no caae exceed 76^ Fahrenheit, and it is preferable to keep It down to OOP or 
70®. 

The dimensions of the brush face transverse to the commutator segments, 
is determineil almost solely by commutation requirements, and these in- 
volve so many widely varying factors that no hard-and-fast general nda 
can be laid down. For machines of ordinary types and fftlrlj large sixes — 
100 kilowatts and over, say — the span of a carbon brush may be roughly 
estimated by means of the formula 



PBACTICAL DTNAHO DESIGN. 



TUi lonnBlB vUl sppl; vlUi infllcli 
iwiliilin tb« mlng, for % ilrwi tjim v uoiku, u> iiki 
duomlnator of ths brmoketAa (rmctlon. For toT«n]ne m 
tipe. (or ujunple, it b ISOO. ud for aiiul], ■tLiuK^vound i 
tliBul dfalfu, ft iMBgtt from SOO to 1000. 

Alr-^kmf. — Tile mschuilcal slr^np, trom tba pole-fi 

tkeumUureueth, ibonld be made the 

thM ilreai bj the fonnnlm 



for >11 pneUokl work bj 

of th« oo«flelont In tbe 
ling molon of « certain 



nB,UtlMfoni 

micUne ii to r 
HDldbeAlnch 
nadiUiinaer U 



Iktphiiof . 
pTvnbury 



[hs bwla of thli uctloD. Bea"CheoklDg op 



iwlovlj described, Ihe aTerafo chord b^ng oqiul i 
pBiUel lo the ahart being prefenblT equal to Uie ch< 
II ._ii.i — 1-1 — 1 .I. Intetpolar edge* 



3 jU /)> and Ihe wldtb 



F^llj oblli 



ha aimatnre slota. A common expedient tor avoiding Ihli par- 
lo round the Inlerpolar edges M In Pig, 36, or to make them 

rwlth npoot to the aiK of tha machine, u In Fig. ST. If 
vKbont ahoe* are DMd, (he eonnn at alternate eheeli of 




I 



•MihooldbeentswaTaalnFIg. tS f > 
*- Id I^. 3«. for polar ■ilesair— 
tv..___. 3f fh< '— --- 



- in nf. w. lor polar ■itesalona. 

ibtlanrth of the pola-taoe epan ihoald never exceed 2.6 I>,-^p; prMtl> 
olnluaareglTan In the beginning of thia aeetlon (pageSM.) 

Checlilac "r grgU»tiM»ry PI»«iiaal»M.— Before pagalngon to 
Ibe Deld-mignat proportlooa, and proftrablj ba(or« taking up the probable 
■"Batna Icnea, the prallmlnair dlmenalona ahoald beobaakad ap In order 



atna Iceae*. the prallmlnaiT dlinenaloni 
uka inre^Mt tbe dealred E.M.F, la o 
—■ aolalling tl ' ' 



iia oeinaeaea np inoraer 

able at the dealred apead 



364 DYNAMOS AND MOTORS. 

HftTing ascertained by meana of eq. (11) the maximtun niimber of coQ 
sIotB allowable and adjusted the net armature iron dimension axiaUy W 
eq. (12) the £ Ji.F. or counter KM.T. of the armature should be tested by m§ 
formula: 

„ __ k^D^^Wp^N. r.p.m. IQ-* ^^ 

P5« ^ 

and if the E.M.F. is not what is desired, the armature diameter should be 
changed to correct it rather than change the value of either Wp or ^ or both. 
On the basis of the author's method, the E.M.F. is proportional to hj^^. if it 
be assumed that the number of wires will increase or diminish in proportioa 
to small variations in the diameter ; therefore, if the preliminary dinieB> 
sions do not {dve the proper E.M.F., the correct dimensions may be clQeoTr 
approximated by 

Trial ZV-w xE ^ ^ ^ ^^ 

5^2P = Correct ly--; 

the word ** trial" referring to the diameter and E.M.F. first obtained. 

If the air-gap length actually adopted is not precisely the value given by 
eq. (28), the pole-face density snould be adjusted to satisfy the equMion, 

P^- p6 <"^ 

The values Of k* and kd are as follows : 

Type of Machine: General Service. coST^e^g. ^^'S^' 

!:•= 81 86 96 

kd=z 1662 16B2 1831 

The tendency to field distortion and sparking at the brushes should also 
be checked (after correcting the armature dimensions and pole-f aoe density 
as just explained)_before taking up the field magnet propornons. 



pS is approximately proportional 
-gap, and ii ilT* dr ~ P = Armature 
nder each pole-face. 



Arasatnre lt«ac«ioB sutd CoMHiBtatloB. — • In order to guard 
against excessive field distortion the relation between the air4ap ampere^ 
turns and armature ampere-turns should be as indicated by the following 
formula, for operation with fixed brushes at all loads : 

Bfpa^lvl.Jr«^ (31) 

The value of A> varies as follows : 

In general service machines, kr n 2.8. 

In ahuut and compound reversing motors, Jv ^ 8. 
In series-wound motors, kt « 2.7. 

The formula is based on the facts that Bp2 
to the ampere-turns required bv the air-ga^ 
ampere-turns tending to distort the field under 

Tne tendency to sparking at the brushes is proportional to the inductance 
of each coil, the number of coils simultaneously short-circuited by one 
brush, the number of coils in series between one positive and one n^atlve 
brush and the current in the coil being commutated, and inversely pnmor- 
tional to the length of time the coll Is short-circuited by the bmsn. The 
inductance of the coil is proportional to the length of the conductor and 
the square of the number of turns per coil. The following formula, based 
on these considerations, is an excellent criterion as to the sparkleasness of 
a machine : 

(Fr« + 0.1^)<«t.n*^|r.p.m.lO-«-Z» (3^ 

The value of Kt varies as below : 

Kilowatts of machine : Up to 15 30 80 100 600 1000 or over. 

Kk= 80 70 00 00 40 86 

Field MLmnmt. — Gores of circular cross section are most economical 
of wire in the field windings, and a square cross section is next best In this 
respect. The temperature rise is greater, however, in a round eoll ot given 



P&ACTIO^Ii DYNAMO DBSIGN. 365 

Miignfitiring nmrnr Ihan in a squure one, the oroes seotloii of the core and 
lenifh of coilalonf the core being the same in both oasee. Bound ooila are 
cnSer to windy and are nenally preferred. ^ . . 

The length of a magnet core from the yoke to the pole-shoe or beginmng 
of polar extensions, £«., the space available for windings, parallel to the 
§ax path In the core, may be roughly estimated for prel iminar y Uying^ut 
MfouowB: 

jU = . ^^ ._, (38) 



900 



o.3 4pap\ 



V "^ UN. 



The trial core length obtained by means of this formula will nsnaUy require 
rwrteion in ordorto obtain the proper radiating surface for the coils. 

Tkt nagneiie densUy in field-manciet cores ranges from 90,000 to IQOfiOO 
lines per square inch for cast steel, and from 100,000 to 110,000 for sheet 
itoel. The density in magnet yokes ranges from 3&,000 to 45}000 maxwells 
periqiiare inch in cast iron, and 85,000 to 05,000 for cast steel. In railway 
motonand others of extraordinarily light weight, the yoke density is con- 
Bidenbly higher than in stationary machines ; the core density is also 
Mmsvhat higher, bat the dUference is not so great as in the yoke. 

The density is not uniform throughout the length of path in the core, nor 
bit 80 in the yoke, but for conyemence the maximum density is assumed 
to eiist fhionghout the length of each path. 

Lmkage of magnetic Imes between adjacent poles and between each iwie 
ud the yoke surfaces makes the flux in the field magnet considerably 




1 



FlO. 40. 

rMier tiiM^ that in the airgap. The relation between the magnet-core 
In tad the air-gap flux is 

TheTslue of r varies widely with different types of machines and different 
liiM of a glTen type. Tot well-designed machines of conventional types it 
■sf he assumed tentotively to have the values given in Table X. It is con- 
lUerably higher for poor designs. In the absence of data from existing 
■ashlacs ofthe type being desiened, the field magnet may be proportioned 
on the basis of the values in Table X, page 870, tentatively, and the leakage 
nMighl J cheeked up as follows: 

Lay out to a rather large scale two poles of the machine and the corre- 
■ponJliig portion of the yoke, as shown in Fig. 40 for a circular joke. The 
nengelraisth of the leakage path between the uoper surface of the polar . 

•xteSkm and the inner surface of the yoke wlU be about as indicated by M 

the dotted line Z, and the length of the leakage path between the neighbor- m 

tag polar extensions wUl be about as shown by the line Z,. The mean ^ 

^gth of the leakage path between the flanks of neighboring pole-ends is \ 

pncticaUy eqwOto the dtotance between the centers of the two measured 
•long a cinr^ar arc concentric with the armature ; repreront It by Z,. 1 Je 

mm length of the leakage oath between each Po\tP*2'**SS"^!^1™«S7fl„5 
nriaceWng between «Mid» may becalled equal to Z. The maximum flux 

fa the ma^t core will be approximately as given by the equation, 

VleM-Manie* Kxcttaitloia.— In order to estimate ^^^o'^^fj^ *52 
•wsltatton required by the machine, the quaUty of the Iron and steel to be 



» 



Aoipent-tumi p«r Incb of lausth 
ir-gap of > dyiiamo U no load 1* 



PRACTICAL DYNAMO DESIGN. 367 

For a motor tbe flu is the same at fall load m at no load, except in special 
Cises where a series winding is used in order to start a heary load, and ex- 
e^»Ung series-wound motors. The maiimnm air-gap flux for a motor haying 
to itart under a load is 

^-^-inpiaN. ^ 

The full-load ampere-turns per pole for a dynamo or motor are ^-4- iV. 

The ampere-tums per inch fbr the armature teeth will be the mean be- 
tvcm the ampere-tums per inch required to produce the density at the tops 
and those required to produce the density at the roots —not the ampere- 
tuns required to produce the average density in the teeth. The approxi- 
msts dmsity at the roots of the armature teeth will be, at full load, 

and flie approximate density at the tops of the teeth will be 

Ai tome of the flux passes to the armature core body through the slots 
ind ventilating spaces, the aetual densities in the roots and tops of the teeth 
an k» than the approximate densities given by the above formulas. The 
aetual densities cannot be computed directly, but may be derived from the 
niatioh between the actual ana approximate densities, which is as follows: 



Br'=Br + 3.1i«A[^'(l+J)-l] 



(40) 



Sbee the fonnula cannot be transposed to solve for Br l>«oause Br *°<l/r 
■re interdependent and vary at different rates, a table should be prepared 
■bowing values of B/ corresponding to different values of /^ at different 

ratioa of « -^ r and Wm -4- w. The preparation of such a table is greatly 
fsriHtsted by first preparing a table of values for 

Npreaenting this expression by Jb^, and thereby reducing eq. (40) to 

B/=Br + *r/r («) 

Table XI, page 377, gives values for kr for practical ranges of values for the 
tvo ratios mentioned. From eq. (41) and curves such as those in Fig. 41, a table 
of eorreaponding values for Br' <^<^/r ^ easily prepared. From such a table 
the Tslue of /^ should be ascertained for the root and top of the tooth and 

also for two or three equidistant intermediate points between the root and 
Vofr* the average of these will be the working value. 
The ampere^nms per pole required by the air-gap will be 

r,= »^"" V . — r w 



i 



<»F>+»*.*.»(^+*») 



368 DTNAM08 AND MOTORS. 

Table IX, page 37S, giTM TslDMot tt, »"> ^- *1 >>"■ tli«flo' i^l vltUn otdt 

atrj natgtm. Ths coneUnt kn la Dierel; Ibe number wblch, mnlUiilisd b 

tfae Blr^sp lenffth, fiTet the extent to Tbkch the atr^^p dimenBLon pai«I*~ 

' (0 tbe iban U luureMtil bj the boving OQtvud ot tti« masnatlo fliumpi 



« 



> 



tog troin the t^le-faoe edgei to the umalure core teeth. The oonttMit ki l< 
the proportion ot the pbytlcal Blr-up length. J, by vhl^ the gmp ts inenOMl 
etfflctWeLy by the pbiBii^e of flux mto the iJdH of the ftrmmfnre cere teeth. 
Thlshu been uken from Mr. F. W. Carter'* article Id the Bledrical WarU 
and Engincrr tor Nov, 90, igoi. 

The THlue of F- csunot be predetermlQed aith any approach t« aoemraey 
luilflfle one baa data from exlitlna niaoblnee of oorreeporullng tjpe and oD^ 
pnt. The following empirloal formula vlU eerie bi eitiniaM nnghly tha 
Talue otJ'-{-Fr for modern Amerloan dynamo* and non-rererdng moton : 



^ 



PRACTICAL DYNAMO DESIGN. 3g9 

J-+^.= <^-^'"^-»»>*'^'+i/i^«+(^-»*^^'V . . (48) 
iy»«T«»ing motor., ^___1 ^ ' ' 

F+Fr= J^tj^ /aejfr*;^ (4aa) 

The no-load excitotion of a ahunt-wound dynamo need not be predeter- 
Dined. The no-load exeitation of a oomponnd-woimd dynamo is 

Tlie ampere-tnms of the MTeral parts of the mag netio oirovlt are deter- 
BdDed M in the case at full load, taking into aooount the difTereneee in 
magnetie density in each part. 

iuter tiie first machine of a giren type has been constrnoted, with the 
ezetttUm of the fleld-magnet coils, it should be tested with temporary 
fixdyng ooils ; the resnlts of these testa should be taken as the foundation 
of the magnet coil calculations. 

rield-BEaiC**^ WIb^Ibm. — The field winding of a series or shunt- 
vmind dynamo must be capable of giying the excitation required at full 
losfd. 

The field winding of a shunt-wound motor must give the excitation re- 
quired at the proper full-load speed. 

The field wmdmg of a series-wound motor must gire the excitation re- 
quired to produce the starting flux, •,. 

The shunt winding of a oomponnd-wound dynamo must glTe the exoita- 
tka required at no Toad ; the series winding must gire the difference be- 
tween this and the exeitation required at full load. 

The shunt winding of a oompound-wound motor must gire the excitation 
required at normal no-load speed ; the series winding must give the difiTer- 
saea between this and the excitation required to produce the starting flux, 

Iha surface of any field magnet coil on a dynuno or motor of open con- 
itmetion (non-enclosed frame giving the external air free aoceaa to the 
vindin^), should be 

IfO^^ (44) 

r bebig the resistance of the coll when warm. For enclosed or poorly Ten- 
tilated frames, the coll surface per watt per degree of temperature rise 
mait be determined by trial ; no general rule wUl apply. In all oases 0/ 
ihould not expeed 70^. 
The proper slae of wire to be used in a shunt field coil is approximately 

^ _ ^M(g + irA) ^^ 

Should the calculated ralue of cP not correspond with any standard sise, the 
aearest standard slxe should be adopted and the depth of the winding ad- 
Iwted to suit it by transposing eq. (45) and solyiug for A, thus : 

d*e 

£,^— («) 

ir 

Bee also Magnet Windings, page 112. 

The minimum number of turns per pole for the series coils of a com- 
poand-wonnd machine is 



Turns = 



Iw 

or 
^+ ^; - ^'* (long shunt) 



(47) 



» 



DYNAMOS AND UOTORS. 



sot nceed OiXIIB tmn 
lb per *4n[Mro ordluirllr ; It w\u ba fiiuIlT deCerniliMd kr 



« per ■mpATB ftotiuil; canied b; tl 



tbechnrnftrr-.f norrlM, Table XII, jmm y... ,.,_ 
dlnsry coiistHiit-potBDlUI dynrnmia, ■nd>rg. Wglrdi 
'ton for genBral nerTice. Traotluu md nutonioHls » 
I7 from ftiHa laluea. 



A trUI pol&r bore, eq- S or 9 or 10. 
TypoofurmiHurB wfndlnB: numborof pull 
Numbar of polM ; eq , 6, for Isp-wonnd niM 
Hatio of pole-fauB span : pols pitcb (#). 
Mulmuin pole-f ue iridth (W,^bi. D,). 
Alr-gsp, eq. 26; the Brmalnre dluneter fell 

k Tri™i^^o( ooDductor, Wble VI.' 



1 



PRACTICAL DYNAMO DESIGN, 



371 



9. 



Sixe of eo!l slot, based on number of conductors per Blot, either 
Table HI or eq. 13, and rulee« <28 and « =- to— . 

10. Possible number of coil slots, eg. 11 ; hence, total number of armar 
tore conductors, keepixig in ylew type of winding, eq. 2. 

11. Corrected poie-faoe density, eq. 30. «. .^ , 

12. Field-distorting armature reaction, eq. 31; if *> comes out too 
■mall, the polar bore must be increased, thereby increasing the pole-face 
dsnstty and air-gap ; then solve eq. 31 for A;, taking the nearest smaller 
Tslne chat will lit the winding. ^ ^ ,». .* *v i^ 

13. Corrected pole-face width, by soMng eq. 29 for Wp; if the result 
5 ** 23^ accept it ; if not, take a stiU larger polar bore, with the corre- 
nondiBg air-gap, and start oror from Determination No. 11. 

14. Net axial iron measurement in annatiure,eq. 1^ , .,,. ^^^^if^^ 

15. Groes length of armature core (= Wpf2lXo FTp + 4 1) ; ttie dlffer- 
«DC8 between tWTand the net iron to be o«caPj«d by ventilating ducts^^^ 

18. Number of armature ooiU ; check by Table IV roughly ; a discrep- 

SMyof 25% is not prohibitive. ^^ . «« »^ u »^ - «- 

17. Diameter of commutator barrel, eqs. 21 and 22 ; Z)» should never ex- 
QMd0.9Z^, andO.7 />• is an excellent limit: if the diameter comes out too 
great, the number of armature colls must be reduced and the axial dlmen- 
•ions of the machine increased correspondingly, if practical : if not. a larsrer 
poUr bore must be Uken and the determinations revised from No. 11, also 
rfnsingtheair^apbyeq.28. _^ ^ « ^ ^ «t 

13. Complete commutator and brush dimensions, eqs. 25, 26, and 27. 

19. Probable tendency to sparking, eq. 32 : if Kk is excessive, and the 
tsms per coil cannot be reduced without entailing an unwieldy number ox 
oaib, the polar bore must be Increased in, order to permit reducing the 
lM|th of the armature core, the determinations being revised from No. 11 
•ft«r finding the new air-gap, eq. 28. 

». Armature losses with respect to heating, eq. 15 et seq. ; if P^' ^- 

ewds the limit set by eq. 14, and cannot be brought within the limit by re- 
doelng the hole in the center of the core, the ventilatinK ducts may be 
redaoed sufficiently to accomplish the result ; if not, and if Wa cannot be 
•sfBdently increased on account of eq. 32, the polar bore must be increased, 
the corresponding air-gap adopted, and the determinations revised, begtn- 
BlnfwithNo.il. 

luvimr progressed this far, the remainder of the desiffn is straight work, 
only a slight revision of the trial magnet core length beingprobaDly neces- 
nrv to oDtain the Tniniiniim quantity of Aeld copper within the neatlng 
lioilt. 

VAJDMJB I. 

Valvea of Im. 



Poles. 


^ 1= 0.066. 


4r = 0.7. 


^ = 0.72. 


4f = 0.75. 


2 

4 
6 


0.866 

0.5 

0.342 


0.891 

OJ5225 

0.3684 


0.9048 
0.5358 
0.3681 


0.9239 
0.56S6 
0.3827 


8 
10 
12 


0.2588 
0.2079 
0.1736 


0.2714 
0.2181 
0.1822 


0.279 

0.2244 

0.1874 


0.2906 
0.2334 
0.1961 


14 
16 
18 


0.149 

0.1306 

0.1161 


0.1564 

0.137 

0.1219 


0.1609 
0.1409 
0.1253 


0.1676 
0.1467 
0.1305 


20 
22 
24 


0.1046 
0.QM9 
0.0872 


0.1097 
0.0998 
0.0915 


0.1129 
0.1026 
0.0941 


0.1176 
0.1069 
0.0979 



i 



DYNAHOe AND IfOTOBB. 



Ill 
3-1 

« 
I 

3 111 
9 



I 



■<«Ifl"I*, 


„. 


-""SssaxasKssa 


i 

3 
1 


1 
1 

1 

1 
1 

1 

1 


" 




: : : : :»3«iii»ss*« 


= 




:::::: :S35?>iiii! 


S 




■ '■ ■■S5S=5'i""^=5« 


S 




: : : : :5^s?si:i5«? 


• 


i!S:353S"*5''<'^^^' 


• 


3S53S'*5^"5???,.=.^^ 


- 


|S«i!i;88*?fl?^Si^H?? 


- 


?????!!,<wi?^,.s ; : : : 


■«l6"!il. 


— ""■•■ sssassassaa 


1 

3 
1 

■s 


1 

■8 


- 








. 








- 


: : : : :!?ss?>.ii!i^s?r!ii : 


t. 


: : : : :3S!i!*?«ii!iS!!ii!!i : 


« 1 ;;^S«4li<;^S!>|Ii«!)3t!tS! 1 


& 


!j3SS!S!l?«Si5(!Sass!!I|i! 


- 


ssii^asajsaaas :::::: 




18 911 


a 


... 


"•"asHHsasaaaa 



^ 



FRACTICAL DYNAMO DESIGN. 



373 



Trial Jkwmmtmrm G«ll Mot Depths. 



Cora Diameter. 


Slot Depth. 


Gore diameter. 


Slot Depth. 


6 

? 


ft 


1? 
11* 


S 




H 

Ift 


12 


i? 




k 


If 

15 


1? 



Vvtal ▼•!«•• for MfniaauM Vwamh^r •f Amature ColU. 

The nnmberB in the table are Talaee of ^^ X -^KW.* 



KW.» 


125 TOltB. 


260 volts. 


600 TOlts. 


1 


11.2 


16.8 


24 JS 


2 


14.1 


19.9 


80.9 


8 


16.1 


22.8 


85.3 


4 


17.8 


25.1 


38.9 


6 


19.1 


26.9 


41.9 


6 


20.3 


28.7 


44 J» 


8 


22.4 


31.8 


49. 


10 


24.1 


84.1 


62J 


15 


27.6 


89. 


60.4 


20 


80.4 


42.9 


66.6 


25 


82.7 


46.2 


71.6 


90 


84.7 


49.1 


76.1 


40 


88.2 


64.1 


88.8 


60 


41.2 


68.2 


90.2 


80 


43.7 


61.9 


95.9 


75 


47.1 


66.7 


103.3 


100 


61.9 


78.4 


113.7 


126 


65.9 


79. 


122.6 


IfiO 


60.4 


84. 


130. 


20O 


66.4 


92.6 


143. 


960 


70.4 


99.6 


154. 


30O 


74.8 


106.8 


164. 


400 


82.4 


116J» 


180. 


GOO 


88.7 


125. 


194. 


flOO 


94.3 


133. 


207. 


TOO 


99.3 


140. 


218. 


800 


103.8 


147. 


227. 


1000 


112. 


158. 


246. 



•KW. 

Fbr» = 2 
^pf^ = 1.4 



Kilowatts output of dynamo or intake of motor. 

4 6 8 10 12 14 1.6 

2.4 3.36 4.2 6 6.8 6.6 73 



i 



r 



374 



DYNAMOS AND MOTORS. 



Vrtal ValmM for Maximim Allowable Mi 

A.nM»t«re Coll. 



ibor of It 



Formula : /> ^ 240 9 -p Up. 



Lap 
Winding. 


Two-path Windings. 


Torus per 
Coil. 


p = g. 


/, = 4. 


|> = 6. 


p = 8. 


1 


i. 


U 


U 






240 


120 


80 


60 


1 


60 


30 


20 


15 


S 


26 


13 


9 


6.6 


3 


16 


7J5 


5 


8.75 


4 


9.6 


4.8 


3.2 


2.4 


5 


6.6 


3.3 


2.2 


1.66 


6 


4.9 


2.4 


1.6 


1.22 


7 


3.75 


1.87 


1.25 


0.03 


8 


3 


1.5 


1 


0.75 


9 


2.4 


1.2 


0.8 


0.6 


10 


1.8 


0.9 


0.6 


0.45 


11 


1.66 


083 


0.66 


0.42 


12 


1.42 


0.71 


0.47 


0J5 


13 


1.22 


0.61 


0.41 


0.3 


14 


1.06 


0J63 


0.35 


0.26 


15 



^ 



PRACTICAL DYNAMO DESIGN. 



375 



TAJIII.V VI. 

mm for Carrytef Cmpm^ity of Ai 

2 or 4 Wire* in Parallel Considered a Single Conductor. 



Bonnd Wires, Drawn to B. A 8. Oange. 



No. 



n 

M 
15 

H 

13 
» 

11 



I 

7 
6 



2 


4 


in nar- 
alieT 


inpar- 
aliS. 


No. 


No. 


• • 

• • 


* • 

• • 


• • 

90 


• • 

• • 


19 


■ • 


18 


• • 


17 


20 


16 


19 


16 


18 


14 


17 


IS 


18 


13 


15 


11 


14 


10 


13 


9 


12 


8 


11 


7 


10 


6 


9 




8 




7 




6 



IM X r.p.m. s= 



4000 to 

eooo. 



8000 to 
10.000. 



Amperes. 



2 

2i 
S 

4 
6 
6 

71 
9 
U 

\^ 

17 
21 

26 

m 

40 

62 
66 
80 

104 
130 
160 



5 
6 
74 

I 



33 
40 
60 



80 
100 

132 
160 
200 



Rectangular Conductors. 



/>• X r.p.m. =r 



10,000 to 


16,000 to 


12/100. 


17,000. 




• 


o 


o 


« 


.a 


« 


« 


s 


s 


O" 


c 


a 


« 


i 


1 


S 


s 


1 


i 


9 


i 


^* 


i 


«M 


«4 


o 


o 


►» 

«» 


^ 




"S 


A 


A 


•d 


•o 


*» 


•*• 


a 






p 


O 


o 



20,000 to 
22,000. 



•8 



i 

I 
i 



a 



c 

I 



376 



DYNAMOS AND MOTORS. 



From ** The Dynamo," by Uawkliu A Wallis. 
V»1«M Of k,. 



a 


J=«. 


5: =10. 


2=12. 


}=^ 


J-". 


0» 
100 

W> 
909 
B09 


1.96 
1.86 
1.76 

1.66 
IM 
1JS2 


2.18 
2.06 
1.96 

1.84 
1.75 
1.606 


2.38 
2.23 
2.10 

1.98 
1.89 


2.66 
2.38 
2.26 

2.12 
2.00 
1.90 


2.7 
2.6S 

2jn 

2JM 
2.12 
2i» 



Poles = 


4 


6 


8 


10 


12 


14 


16 


18 


20 


km = 


0.8 


0JS6 


0.42 


0.36 


0.3 


0.9RA 


0.226 


0.2 


0.18 



ai6 



From " The Dyxuuno/' by HawkinB ft WaUis. 



Wd— Wp _ 

a - 



1 
0.74 



1J( 
\J0 



2 
1.2 



2JS 
1.88 



3 
1.64 



9Z 
1.68 



4 

1-8 



Avenic« Magvetlc Iieakac« Go«iiel«ati. 



KUovaUe = 


10 


26 


40 


60 


75 


100 


200 


300 


600 


1000 


" = 


1.36 


1.3 


1.27 


1.26 


1.23 


1.2 


1.18 


1.16 


1.13 


1.12 



PRACTICAL DYNAMO DE8ION. 



377 









ValvM 


•f k^ 








f 


'^•-i.ie 


1.17 


1.18 


1.19 


1.20 


1.22 


1.24 


T 


MA 














0.^ 


3.10 


3.16 


8.21 


3.26 


3.32 


3.43 


iJA 


0.75 


3^ 


3.34 


3.4D 


3.45 


3.51 


3.62 


3.73 


dflO 


3.47 


3JS8 


3.59 


8.64 


3.70 


3.82 


3.93 


ftiS 


3.06 


3.72 


8.78 


3.84 


3.88 


4j01 


4.13 


aso 


ZM 


3.90 


8J6 


4.02 


4.09 


4.21 


4.38 


QJ96 


4.03 


4.09 


4.15 


4.21 


4.28 


4.40 


4JSS 


1J» 


4.21 


4.38 


4.34 


4.40 


4.47 


4.60 


4.72 


IJB 


4.40 


4.46 


4.63 


4.60 


4.66 


4.79 


4.92 


U8 


4.58 


4.65 


4.72 


4.78 


4.86 


4.96 


5.12 


U5 


4.77 


4.84 


4.91 


4i»7 


5.04 


5.18 


5.32 


UO 


4.96 


5.02 


5.09 


5.16 


5.23 


6.87 


5.52 


136 


5.14 


5.21 


5.28 


5.35 


5.43 


5JS7 


5.71 


1^ 


6^ 


5.40 


5.47 


5JS4 


5.62 


5.76 


5.91 


L3S 


5JS1 


5iS6 


5.66 


5.73 


5.81 


5.96 


6.11 


140 


5.69 


6.77 


5.86 


5.92 


6.00 


6.16 


6.31 


\A6 


6.88 


6.96 


6.04 


6.11 


6.19 


6.36 


6.51 


liO 


eM 


6.14 


6.22 


6.30 


6.88 


6.64 


6.70 


tSB 


6.36 


6.33 


6.41 


6.48 


6JS7 


6.74 


6.90 


lA 


6.43 


6.52 


6.60 


6.68 


6.77 


6.98 


7.10 


\M 


6^ 


6.70 


6.77 


6.87 


6w96 


7.18 


7J» 


UD 


6^ 


6J9 


6.96. 


7.06 


7.16 


7.32 


7.40 


US 


6J0 


7joe 


7.17 


7.25 


7.34 


7.62 


7.69 


liO 


7.18 


7.26 


7.36 


7.44 


7J» 


7.71 


7.89 


i IJS 


7.36 


7w46 


7i»4 


7.63 


7.72 


7.91 


8.09 


! »•» 


7JS5 


7.64 


7.73 


7.82 


7.92 


8.10 


8.29 


i 2410 


7.92 


8i>l 


8.11 


8.20 


8.30 


8.49 


8.68 



TABUB 







ApproprUte DUtributlon of XjOmoi 




• 




in Per Cent. 




•a 


3 


*^^ 






*i*t 


1 


Annatore Lofges. 


2 • 


■ 


dp 
gH 


o 






Si 


1 


Per 

Lom; 


M 










Copper. 


Iron. 


1^ 


30 


90 


44) 


8.0 


2A 


0.5 


10 


40 


90JS 


3.8 


2.8 


3.4 


0.5 


9JS 


60 


91 


3.6 


2.7 


2.8 


0.4 


9 


75 


91Ji 


8.4 


2JS 


2.2 


0.4 


8.5 


UO 


92 


8.2 


2.4 


2j0 


0.4 


8 


200 


93 


2.7 


2.15 


1.8 


0.35 


7 


300 


98.5 


2JS 


2.0 


1.66 


0.35 


6Ji 


600 


94 


2.3 


1.8 • 


IM 


0.36 


6 


TSO 


94.6 


2U» 


1.7 


1£ 


0.3 


5.5 


1000 


96 


1.8 


IJ^ 


1.4 


0.3 


5 






378 TESTS OF DYNAMOS AND MOTORS. 



TSftTS OF DYlTAHOft AITO HOTOBA. 

All reliable manufacturers of electrical maclilnery and apparatus l. 
provided with the necessary facilities for testing the ef&ciency and 
properties of their output, and where the purchMor desires to oonfixm 



tests and guaranties or the maJcer. he should endeavor to have nearly. 
In some cases all such tests carried out in his presence at the factory, uz 
he may be equipped with sufficient facilities to enable him to carry out '. 
tests in his own shops after the apparatus is in place. 

Some tests, such as full load and overload, temperature, and insuli 
(except dielectric) tests are best made after the macninery has been inst 
and is in full running order. 

Owing to the ease and accuracy with which electrical measurement* 
be made, it is always more convenient to make use of electrical drii 
power for dynamos, and electrical load for the dynamo output, and in 
case of motors, a direct-current dynamo with electrical load makes the ~ 
load for belting the motor to. 

No really accurate tests of dynamo efficiencies can be made with iratap^ 
wheels, and only slightly better are those made by steam-engines, owlM 
to unreliability of friction cards for the engine itself and the change of £rl»>{ 
tion with load. | 

Where it is necessary to use a steam-engine for dynamo testing, mil Mss 
tion and low load cards should be taken with the steam throttled so low m\ 
to cut off at more than half stroke, and to run the eng;ine at the same speolj 
as when under load. 

The tests of the engine as separated from the dynamo are as follows :— 

a. Friction of engine alone. 

6. Friction of engine and any belts and countershaft between it and ths 
dynamo under test. 

Consult works on indicators and steam-ensines for instructions for detep> 
mininff power of engines under various conditions. 

The important practical tests for acceptance by the purchaser, or todete^ 
mine the full value of all the properties of dynamos and motors, are to lesn 
the value of the following items : — 

Rise of temperature under full load. 

lExiulation resistance. 

Dielectric strength of insulation. 

Regulation. 

0\'erload capacity. 

Efficiency, core loss. 

Bearing friction, windage and brush fHction. 

I*R loss in field and field rheostat, 
/■72 loss in armature and brushes. 

Note.— If a separate exciter goes with the dynamo, its losses wUlbe 
determined separately as for a dynamo. 

Methods of determining each of the above-named items will be described, 
and then the combinations of them necessary for any test will be outlinsd. 

V«Hip«rfstar«. — The rise of temperature in a dynamo, motor, or 
transformer, is one of the most important factors in determining the Hfe of 
such piece of apparatus; and tests for its determination should be carried 
out according to the highest standards that can be specified, and yet Iw 
within reasonable range of economy. The A. I. E. £. standards state the 
allowable rise of temperature above surrounding air for most conditions, 
but special conditions must be met by special standards. For instance, no 
ordinary insulation ought to be subjected to a degree of heat exceediiv 
212° F., or 100° C. And yet in the dynamo-roora of our naval ress^ Uie 
temperature is said to at times reach 130° F., or evenhlffher, which leaves t 
small marein for safety. It is obvious that speciflcauons for dynamos in 
such locations should call for a much lower temperature rise in order to be 
safe under full load. 

For all practical temperature tests it is sufficient to run a ma<diine onder 
Its normal full-load conditions until it has developed its highest temperatnrSi 
although at times a curve of rise of temperature may be desired at varioof 
loads* 



TEMPERATURE. 379 

i mauJl djaamos, moton, and transformers, up to, say, 60 K.W., will 

Hiaximam temperature in five hours run under full load, If the teiiH 

«re riae is ncnrmal ; but lareer machines sometimes require from 6 to 18 

•lUuNigh ttxis depeoDds qmte as much on the design and oonstruction 

apiwratiia as on size, as, for instance, the5,000 h.p. Niagara Falls Oen- 

Kaaeli full temperature in five hours. Temperature tests can be 

~ by oTerloadijog the apparatus for a time, tnus reaching full heat 

akorter petriod. 

dynamoB and motors the temperatures of all iron or frame parts, com- 

B, and pole^ieees, have to be taken by thermometer laid on the 

and eoTerea by vaste. Note that when temperatures are taken 

the iiia<diine runmng, care must be taken not to use enough waste to 

the maehine*s radiation. Where there are spaces, as air spaces, 

[re eorea or in the field laminations, that will permit the Insertion 

tkcrmometer. It should be placed there. Temperature of field coils 

rtd te t«Jcen by thermometer laid on the surface and covered with waste, 

Vf taking tbe reaistance of the coils first at the room temperature and 

B while hot immediately after the kecU run. Temperature rise of arma- 

windinsB can be taken by surface measurement and by the resistance 

od also ; although being nearly always of low resistance, very careful 

kj flne flcalTanometer and very gteadf current are reqtdred in order to 

aything like accurate results. 

fom&nla for determining the rise of temperature from the rise of 

is as follows : 

^X v*** ^^ Tcalatance; for copper. — The in- 
due to increase in temperature is approximately 0.4% 

sik degree Cent, above zero, the resistance at zero being taken as the 

If then 

1} = tamperatiire of copper when oold resistance is measured (Cent.), 
' = resiatance at temperature ^, 
, = temperature of copper when hot resistance is taken, 
: reeiataiice at tMoperature f«, 
Snt reducing to zero degrees, we hare 

^ ~ 1 H- 0.0042 ty ^'^ 

' The increase in reaistance from to 1^ degrees isR,'^ R^^ and hence we 
^T« £or final temperature, 

^= ^^^ .f 0.0042 (?) 

ptIistttitUng (1) JZ, (1 -f 0.00*2 tx) — R t .,v 

I ^^ 0.0042 iti - ^*' 

Jt is etftea convenient to correct all cold resistances to a temperature of 
>C, in vbieb case we first redaee to zero and then raise to 20^. 
~ ~ formula for obtaining the resistance at t degrees Is \ 



A = (l-f 0.0042 Qi^. 
R^ rs 1J004 Ko and in terms of the cold resistance at temperature t. 

^""(14-0.0042/} ^' 

<3> then becomes, when the cold resistance is at 20^^, 

first formula requires but une setting of the slide rule, and the sub- 
of the eoastant 238 can usually be done mentally, the advantage of 
equation la tids f ona is very great as regards both speed 



coefflcieiits most generally used are 

0042 

Ybriron 004B 

Par German sUver .00028 to .00044 



380 TESTS OF DYNAMOS AND MOTOB8. 

The following parts should be tested by the resiatanee method and tte 
surface methotralBO : 

Field coUs series, and shunt. 

Armatwre eaiU, In 8-phase machines, take resistanoe between all time 
rinKS. 

llie following parts should be tested by thermometer on the snrfaee : — 

Boom^ on side opposite from steam-engine, if direct connected, and always 
in two or more parts of the room, within six feet of machine. 

JBearingSt each bearing, thermometer held against inner shell, nnleae oU 
from the well is found to be of same temperature as the beazing. 

Commutatorg and collector rings. 

Brvsh-holdera and bruthea^ if thought hotter than the commutator. 

Fole-tipi^ leading and following. 

Armature teeth, windings, and spider. 

Field/rame. 

Terminal block$, for leads to switch-board, and those for leads from tih* 
brushes. 

Series akuntt if in a compound-wound machine. 

Shunt field rheostai. 

On transformers which are enclosed in a tank filled with oU,temperatcmi 
by thermometer should be taken on — 

(hUHde ea««, in several places. 
OU, on top, and deeper by letting down thermometer. 
Winding$t by placiniz thermometer against same, eren if under oil. 
LaminaHontt by placing thermometer against same, eren if under oil. 
TerminaU. 

Boomf as with dynamos and motors. 

Also resistanoe measurements of primary and secondary windings, £roiB 
which the temperature by resistance can be calculated as shown. 

On transformers cooled by air forced through spaces between windings 
ind spaces in laminations, temperatures by thermometer ahonld be taken 
•n~ 

Outside /irune* 

Air, outgoing from coils. 

Aitt outgoing from iron laminations. 

Windings. 

Terminals. 

Boomt in two or more places. 

Also resistance measurements, hot and cold, should be taken, from which 

rise of temperature by resistance can be calculated. 
Finally, the cubic feet of air, and pressure to force same through qmums 

(easily measured by " U " tube ot water), should be measured. 

When other fluids are used for cooling, such as water passing through 
piping submerged in oil, in which also the windings and core are submerged, 
or through windings of transformers themselves (made hollow for the pur* 
pose), the temperature of incoming and outgoing nuid should be measured, 
the quantity used ajnd the pressure necessary to force it through the path 
arranj^ed. besides the other points mentionea above. 

Careful watch of thermometers is necessary in all eases, as they will rise 
for a time and then begin to fall : and the maximum point is what u wanted. 

British authorities state a demiite time to read the therm<mietera after 
stopping the machine. 

Care must also be taken to stop the machine rotating as soon as possible, 
so that it will not fan itself cool. 

A handy method of constructing a curve showing thexise of temperature 
in the stationary parts of a machine at full load is to insert a smau eoil of 
fine iron wire in some crevice in the machine in the part of which the tem- 

Serature is desired. Connect the coil with a mirror galvanometer and 
attery. 

The temperature ooeffloient of Iron is high, and the gradual increase in 
resistance of the coil will cause the readings on the gammometer to grow 
gradually less ; and readings taken at regular intervals of time can be 
plotted on oross-eeotion paper to form a curve showing the ehanges in 
temperature. 



TEMPERATURE. 3S1 



Mmemr^m •f tmmnf m r m tm w i««t. — During all heat mna readingi 
•honld be taken erery iuteen {IS) minutes of the following itemt: 

On direct and alternating current nu>tor8 and generators — 

AiDiatiire, Yolts (between the ▼arlous rings where maobine is more than 
single-phase, In the ease of alternators, and between bmshesi 
* in the case of a D. G. machine). 
Amperes (in each line). 
Speed, 
field. Volts. 



On synchronous eonyerters : — 

Armature, Tolts (between all rings on A. O. end, and between brushes on 
D. C. end). 

Amperes, per line A. C. end, also D. C. end. 

Speed. 
Pleld, Volts. 

Amperes. 
On transformers, compensators, potential regulators : — 

Volts, primary. 

Volts, secondary. 

Amperes, primary. 

Amperes, secondary. 

Cycles. 

Amount and pressure of oooUng-fluid (If any Is used). 
On induction motors : — 

Volts, between lines. 

Amperes, in line. 

Speed. 

Cycles. 

•rerlofliA —The A. I. E. E. standards contain suggestions for orerload 
ettsdty (see page 303). 

the writer has uniformly specified a standard overload of 26% for 3 hours, 
sad there seems to be no* especial difficulty in getting machines for this 
ittadsrd that do not heat dangerously under such conditions. 

lMi«l»tl«m tce t « — Insulation resistance In ohms Is of much less Im- 
portsnoe than resistance against breakdown of the insulation under a 
itratm test, with alternating current of high pressure. 

Mske all insulation tests with a Toltage as high, at least, as that at which 
the machine is to be worked. 

The following diasram shows the connections to be made with S some 
external souroe of B.M.P. The formula used is 

J^sresistamoe of voltmeter. .._ 

B = E JiJ. of the external source. nlSm\ 

c = reading of voltmeter eonneeted as in I | ^ 



mce in ohms. unarm " >f 



x= insulation resistance in ohms. Mna^ 



According to the A. I. E. E. standards, 
the insulatwn resistance must be such that Fio. 1. Connections for volt- 
tbe rsted voltage of the machine will not meter test of insulation re- 
aend more tlian rnknp of the full-load cur- sistanoe of a dynamo, 
rent through the insulation. One megohm 
k umally considered sui&cient, if found by such a test. Where one megohm v 

iiipecifled as sufficient, the maximum deflection that will produce that 
Tslne, and that must not be exceeded in the test, may be found by the f ul- 
ioving variation of the above formula : 

BXB 

Itrttia tost.— llie dielectric strength of insulation should be deter- 
mined by a eontinued application of an alternating E.M.F. for at least one 
(I) minute. Tlie transformer from which the alternating E.M.F. is taken 
ihoQld have a current capacity at least four (4) times the amount of current 



382 TESTS OF DYNAMOS AND MOTORS. 

BeoMsazy to olmrge the apparatoB mider test aa ft Aondenter. Btrmln 
■hoald only be made with the apparatus f uIIt assemhled. 
Gonneot on a D.O. machine as in the following diagram. 

Strain tests should be made with a sine 
-., B wave of B.M.F., or with an E.M.F. haTii^ 

nmiaBi\ "K"- ^® ^™o striking distanee between noedle 

P""™^ m points in air. 

L^O/ ^i A^ , .nr .. See article 219 A. I.B.E. standards for 

■— r^rtT. i3« ii»! A. proper voltages. 

^^ ri li*J © lKr«liSo«.-The test for rs«»l*- 
/ \^|>* n o T J *ion in a dynamo consists in detemmiiiw 

^gnAMc — ' tts change in voltage under differaS 

^^ loads, or output of current, the speed be- 

Fio. 2. Connections for strain ingmaintained constant, 
test of dynamo or motor or The test for r^^ulation in a motor 
transformer insulation. consists in determining its change of 

speedt under diiferent applied loads, 
when the voltage is kept constant. 

AtaMdar^U.— For full details of standards of reffulation of different 
machines, see report of the Committee on Standardisation of the A. I. S. E. 
at Uie beginning of this chapter. 

lieff«latloM Testa, Dyaaaios, ftkoat mr CaaspooBA, asiid 

The dynamo must be nm for a suflDksle&t length of time at a heavy load to 
raise its temperature to its highest limit : the field rheostat is then adjvistsd, 
starting with voltage a little low, and bringing up to proper value to obtain 
the standard voltage at the machine terminals, and since a constant temper- 
ature condition ha» been reached, must not again be adjusted during the 
test. Adjust the brushes, in the case of a D. C. machine, for falMoad oon- 
ditions, and they should not receive other adjustment during the test. Tlds 
is a severe condition, and not all machines will stand it ; but all good dy- 
namos, with carbon brushes, will stand the test very well, provided the 
brushes are adjusted at Just the non-sparking point at no load. 

Load is now decreased by regular steps, and when the current has settled 
the following readings are taken : — 

Speed of dynamo (adjusted at proper amount). 
Current in output (a non-inductive load should be used). 
If alternator, current in each line if more than singlei>hastt. 
Yults at macnine terminals. 
Amp«:es, field. 
Volts, field. 
' Note sparking at the brushes (they should not spark any with oarbon 
brushes). 

Readings should be taken for at least ten intervals, from full load to open 
circuit (no load) ; and load should then be put on gradually and by the same 
steps as it was brought down ; and the same records should be made back 
to full-load point, and beyond to 25% overload. 

If the readings are to be plotted in curves, as they always should be, 11 
will make little dilference if the intervals or steps are not all alike ; and 
should the steps be overreached in adjusting the load, the load must not, in 
anv circumstances, be backed up or readjusted back to get regular Inter- 
vals or a stated value, as the conditions of magnetisation change, and throw 
the test all out. In case the current is broken, or the test has to be slowed 
down in speed or stopped, it must be commenced all over again. Finally, 
when the curves are plotted, draw, in the case of a eompound-wonnd ma- 
chine, a straight line joining the no-lemd voltage and the full-load voltase ; 
and the ratio of the point of maximura departure of the voltage from tnil 
line to the voltage indicated by the line at the point will be the reffttiation 
of the machine. 

The readings as obtained give what is called a field compounding enrve. 
In the case of a shunt or separately excited machine, the procedure for the 
test is the same : but when the curve Is plotted, the regulation is figured ss 
equal to the difference between the no-load voltage and full-load voltage, 
divided by the full-load voltage. The curve is called a oharaeteristio la 
this case. 



DYNAMO EmCISNCT. 383 

Par ftltanwion thftt are too large to apply aotiial load as sugfested aboTo, 
■other " no>load '* method eommonlj oned with sattsfaotory reenlts upon 
jllernatori designed upon the usual linee is to short-oirenit the alternator ar- 
■atore upon itself and determine the amperes in the field required to produce 
varmal eurrent in the armature so short-ciroulted^e speed of the machine 
Mni normal at the time ; call this eurrent F, Take anothei' reading of 
%b field eurrent required to produce normal Toltage at the machine ter- 
■faials, with the armature on open circuit and the speed normal ; call this 
nrisnt C. Then the curre nt requi red in the field winding for full non- 

MnetiTeload will be /= Vin+ C*. 

Having calculated the ralue of this current, pass it through the field 
■ladings of the alternator with the armature on open circuit and running 
tt normal speed, and read the Tolts F. Let E = normal Toltage, then the 

Hgnlstien ^ iy ^* 

The current l^is called the " Synchronous impedance *' field current, being 
n named by Mr. G. P. Steinmets, who proposed and has used the above- 
ieKribed method. 

When regulation is desired for a power factor other than unity the field 
wrents >^nd C must be combined at the proper angle corresponding to 
the power factor. For instance, for a power factor ox (i.e., Wfi lag) the 
leld currents would be directly added. This method is used extensiTsly 
nd gfres results agreeing very well with those of actual tests. 



Kttf«lss««m Scats, Kot«rs, Slhwit, ComfcwmA, 

iBdvctlom. 

After drhrfnff the motor under heavy load for a length of time sufllcient 
to develop its full heat, fuil>rated load should be applied, the field rheostat, 
tt toy is used, and brushes adjusted for the standard conditions ; then the 
Mikmld be gradually removed by regular steps, and the following read- 
lap be made at each such stop : — 

Amperes, input. 

Volts at machine terminals (kept constant). 

Watts, if induction motor. 

Speed of armature. 

Koto sparking at brushes. 

Amperes, field (in D. C. machines). 

At least ten steps of load shoold be taken from full-rated load to no load. 

The ratio of the maximum drop in speed between no>load and full-load, 
vlkieh vill be at fuU-load, to the H>e«l »t fnU-load, is the rtgukUkm of the 
■olor. 

XiktCBcx Teste. I^ymamoa. 

As term <|leieii«|f has two meanings as applied to dynamos ; yiz.^ electrical 
J^d ettmmereuU. The eUctriceU efflciency of a dynamo is the ratio of eleo- 
tneal energy delivered to the line at the dynamo terminals to the total electri- 
nlenergv produced in the machine. The commercial efficiency of a dynamo 
■ttwra flo of the energy deHrered at the torminals of the machnie to the total 
■MrS7 fuppUed at the pulley. Otherwise the electrical efilcienoy takes into 
•eeonnt only electrical loss es , while the commercial efAciency includes all 
nvM, electrical, magnetic, and frleUonal. 

Ca r e X caa Teat, aadi T^ut for X'rlctioa and ITlBdisffe. 

T^Mse losses are treated together for the reason that all are obtained at 
ueiame time, and the first can only be determined after separating out the 
«cbeii. 

A eore>loss test is ordinarily run only on new types of dynamos and 
■totoTt, but Is handy to know of any machine, and if time and the facilities 
ve available, should be run on acceptance tests by the consulting engineer. 
U eonsists in running the armature at open circuit in an excited field, driv- 
ing it by belt from a motor the input to which, after making proper deduc- 
"<>Qi, is the measure of the power necessary to turn the iron core in a lield 
01 the same strength as that in which it wiu work when in actual use. 



i 



i 



384 TESTS OF DTKAMOS AND MOTORS. 

Conneot at In tb» f oUowlng diagram, la wliSoh A is dio drnamo or 
under teat, and B la the 




motor driving the 
tore of A hy meana of 
the belt. The Held of A 
muat, of heceMlty, be 
aeparately excitea, aa 
Its own armature olronit 

moat be open bo that 

there may be no current -iKS^SS- 

generated in its oonduo- ■*•*** ^ 

wTB. Fio. 3. Conneotiona for a test of oore Visa. 

The motor field is sep- 
arately excited and kept constant, so that its losses and the oore loea of thaj 
motor itself, being constant for all conditions of the teat, may be «*f^FM^tHttfl 
in the calculations. The motor B should be thorou^ly heated; and besi^! 
ings should be run long enough to have reached a consumt frietlon eoniii* 
tlon before starting this test, so that as little change as possible will tafct 
place in the different " constant" Taluea. It is neeessary to Icnow aoea* 
rately the resistance of the armature, B, In order to determine its I^B loss 
at different loads, and to use copper brushes to practically eliminate As 
/*/{ of brushes. 

It is well to make a test run with the belt on in order to learn at whit 
speed it is neeessary to run the motor in order to drive the armature A at Hi 
proper and standard speed. 

nf ettoB, core l«aa, aiad wtstdagr* of asotor. — The speed havtac 
been determined, the belt is removed, and the motor field kept at ita final 
adjustment, and enough Toltage is supplied to the motor armature to diiTS 
it free at the standard speed. The watts input to the armature is then the 
measure of the loss (I*it) in the motor armature plus the friction of ita bear- 
ings, plus its windage, plus core loss, or the total loss in the motor at no 
load. This is called the " runnins light '* reading. 

I*rictloa asid wiBda|fr« of oynAflso.— After learning the lossss 
in the driving motor, the belt is put on and the dynamo is ariTon at Its 
standard tpeSa without excitation, and In order to oe sure of this a volt- 
meter may be connected across the armature terminals ; If the allghtest 
indication of pressure Is found, the dynamo field can be reversely excited, 
to be demagnetized, by touching its terminals momentarily to a source of 
E.M.F. Take a number of reaolnflpB of the input to the motor in order to 
obtiUn a good mean, and the friction and windage of dynamo la then the 
input to the motor, less the " running light " reading previously ohfalned, 
the I*B of motor armature having been tiken out in eaok oaaa. 

Let P = watts input to motor, 

P. = 7> Jt loss in motor armature when driving dynamo, 
/=** running light " reading of motor, 
/, = friction and windage of dynamo atmature, 
P. = />/{ loss of motor armature when ** running lisdht," 
then /J = p-(Pj4./-p,). 

Brauili friotioa.— The friction of brushes is ordinarily a smalt portion 
of the losses ; but when it is desirable that it should be separated from other 
losses, it can be done at the same time and in the same manner as the test 
for bearing friction. The brushes can be lifted free from the commutator 
or collector rings when the readings of input to the driving motor for bearing 
friction are taken ; dropping the orusbes again onto the commutator and 
taking other readings, tne difference between these last readings and those 
taken with brushes oil will be the value of brush friction. Note, that alIow> 
ance must be made as before for Increase of T*R loss in the motor armature. 

Xoat for eort) loaa. — Having determined the friction and other lossss 
that are to be deducted from the total loss, a current as heavy as will ever 
be used is put on the dynamo field, the motor is supplied with current 
enough to drive the dvnamo at its standard speed, and the reading of watts 
and current input to the motor armature is taken. 

The dynamo field current is now gradually decreased in approximately 
regular steps, readings of the input to the motor being taken at each such 
step until zero exciting current is reached, when the exciting current is 
reversed and the current increased in like steps until tlie hli^est current 



DYNAMO EFFICIENCY. 



385 



_ ta again readied. This may nov be again decreased by Interrals 
;toxero^ rerened and increased back to the starting-point, which will 
complete a cycle of magnetization ; ordinarily this refinement Is not, 
MTi neceBsaxjT* 

test moat always be carried throagh without stop ; and although It is 
• to make the step changes in flem excitation alike, if the excitation 
pad In exoeaa of the regular step it must not be changed back for the 
of making the interral regular, as it will change the conditions of 
'oal Held. When the readmos are plotted on a curve, regularity in 
of magnetization is not entirely necessarr. 
fc4k>wing ruling makes a convenient methoa of tabulation : — 



1 ImiAMO. 


MoToa. 


h 


amperes 
field 


Speed 


amperes 
field 


amperes 

armature 

i 


TOltS 

in 
armature 

e 


L 




Constant. 


Constant. 







OOMPUTATIOHB. 



Itttoia 


Running 


PR 


PB 


Core loss 


Mure, 


light 


Inarm, 


inarm, 
belt oft 




CtOB 


reading 


belt on 


P..-(Pi+/-Pi) 


fm=^it 


f 


Px 


^t 





iw curve with exciting-current values on the horizontal scale, and 
) loss on the Tertical, and the usual core-loss curve is obtained. 



mm mft Core 



iMto K/s««rMls mmA Kddy 



^ due to hysteresis and friction vary directly with the speed \ lossed 

>eddy currents vary as the square of the speed. 

jmx and voltage must now be applied to the dynamo armature to 

I ft M a motor at proper speed, with the current in the separately 
•-ed Iftld kept constant at proper value. Drive the motor (dynamo) at 
r tPodUferent speeds, one or which may be K times the other ; let 

P = total loss in watts, 
/. = loss in friction, 
ir = loss by hysteresis, 
D = loss by eddy currents, or 
/» = A -j- ^4- 2) at the first speed, 
p,-=.Kfy\- KH-\- IPDsX second speed, 



i 



{ 



tr=2,then 



"~2(2— D 2 

sad HoQsman separately devised the above method of separating 
M, but stated them somewhat dUferently. 

ttbe field separately excited at a constant value, different values of 
''are supplied to the armature at dilferent voltages to drive it as a 
. Tke results are plotted in a curve which is a straight line, rising as 
^^<te sre iaereaaed. 



{ 



386 



TESTS OF DTKAICOS AND MOTOBS. 



> 



\ 



) 



The following diacEram shows how the loeses are plotted in curreB. 
test as a separately exdted motor is run at a number of different values 
voltage ana current in the armature, and the results are plotted in a 
as shown in the following diagram. The line a, 6, is plotted from the 
of the current and volt readingi. 

The line a, e. is then drawn parallel to the base, and represente the sum < 
all the other losses, as shown by previous tests, and they may be fi 
separated and laid off on the chart. 

Foueault currents are represented in value by the trian^e a, c, b. 
If another run be made with a different value of ^excitation, a curve, at, - 
or one below the original a, b, will be gotten, according to whether the tot 
losses have been increased or decreased. 

If the higher values of current tend to demagnetise, by reason of the 
currents in the armature, the curve a, 6, will curve upward somewhat at 
upper end. 

it is thus seen how to measure core-loss, and friction and windage cf 
dynamo ■ knowing this and the resistance of the various parts, the emcienc 
is quickly calculated, thus 

Let P — core-loos + friction (obtained as shown). 
V -• voltage of armature, 

■- current of dynamo armature, 
— current of dynamo field, 
" resistance of armature and brushes, 
B resistance of field. 



/ 




■oatH FmoTioii 



■nCTHMMlDWiHOMQS 



9 



Then, considering the above as ihe only loasee (l.e., negleetlag rl 
etc.), jpr 

Efficiency - ——.^—j^^-^p . 

This Is a satisfactory method of getting the effioienoy, bat does not 1 

• ^ In 'Hoad loMes" If 

should exist. 

The simplest meth< 
of determining the 
ciency of a direct-eoi 
machine is to nm it' 
as a motor, without 
or belting or geaiinj 
its proper field streL 
and its proper speed 
measare the mpiit 
the armature, Fran 
value subtract the PI 
loss in the armatare 
the remainder Is the < 
and friction loss. Knoi 
ing this and the 
tance of the remali 
circuits, all the k 
are known, and h«u 
the ef&ciency can be cal- 
culated. This method is 
an accurate one and Is 
easy to carry ont. 

Amother toe* for 
•flcl«Mcy . — 11 the dy- 
namo under test is not 
of too large cMacity, and 
a load for its full output is available, either in the form of a uunp bank, 
water rheostat, or other adjustable resistance, then one form of test is to 
belt it to a motor. 

By separately exciting the motor fields, and running the motor free with 
belt off, its friction can oe determined, and with the resistance of the srma- 
ture known, the input to the motor in watts, less the friction and thei^Je 
loss in its armature at the given load, is a direct measure of the power ^h 

Slied at the pulley of the dynamo. The output in watts, measured at the 
ynamoB terminals, then measures the efficiency of the machine. 



VQCn m ABiumsr 



»^ 



Fio. 4. Diagram showing separation of losses 

in dynamos. 



DTNAMO KFFICnurCT. 



387 



Ii«* P = watts Input to motor. 

Pi = losaes in motor, friction, PR^ and oore-loBf , 
Pi = watts output at dynamo terminals. 

% of e£ELciency = 100 X p^p^ = commercial efficiency. 

Knowing the current flowing in the armature and In the flcldB. and also 
1 »*'T"^*\® resistonce of the same, the PR loBses In each may be calcu- 
lated, which, added to the output at the dynamo terminals, shows the total 
deetrieal energy generated in the 
machine. 

lla-tbe^i21o68 in the armature, ^ - i ne-o 

/ -the P 12 loss in the fields. ^ ' ^^^ 

Ths electrical efficiency in ner- 
cestage wUl be * *« 

Tke adjoining diagram showa the 
eoaaaetlons for this form of test. 

It mat be obrious that a steam- 
€ngIse,or other motiye power that 
can be accurately measured, may be 
JMod in place of the electric motor : 
bet measurements of mechanical 
power are so much more liable to 
vrar that they should be avoided 
vbere possible. 

The only obiectlon to this method 
ttttst the friction of the driving-motor varies with the load, and the loas 
u ths belt is not considered. 




OENERATOR 
UNDER TEST 



Fio. 6. Oonnections for efficiency 
test of a generator, driven by an 
electric motor. 



Kftpi^s TMt wltk Tw« Slflsaar JMract-Cvn^at DjaaaaiM. 

Where two similar dynamos are to be tested, and especially where their 
e^»clty is so great as to make It difficult to supply load for them, it is com- 
"jjp to test them by a sort of opposition method ; that is, their shafts are 
•{•■«r «>i>pled or belted together, the armature leads are connected In series, 
we leki of one is weakened enough to make a motor of It ; this motor drives 
8f ^•iS'' ">»«*>*'>« a» * generator, and Its current is delivered to the motor 
I u ^w^nco in currents between the two machines, and for exciting the 
i«NB of each. Is supplied by a separate generator. 

The following diagram shows the method of connecting two similar 



SWITCH 




{ 



Fio. 6. Connections for Kapp*B method of efficIenoT 
test of two similar dynamos. 



388 



TB8TS OF DYNAMOS AND HOTOBS. 



dynamo* for Kapp's test. D is the dynamo ; M the machine vlth fteld 
weakened by the reslstanoe B, that acts as a motor, and O Is the goneracor 
that supplies the energy necessary to make np the losses, excitation and 
differences. 

Start the combination and get them to standard voltagOf as shown by the 
Toltmeter : then take a reading of the current with the switch on 6, and 
another with the switch on a. Xet the first reading be m, and the seoond < 
and let x be the efficiency of either machine, then 

Per cent efficiency of the combination = 100 x -ft <uid 



=V(ioox^). 



In using this formula the efficiency of the dynamo at its load is aasumsd 
the same as the motor at its simultaneous load, which is usually true aboie 
the I load point. The loss in motor-field rheostat should also be allowed for. 
Another similar method, called **pumpinq back," is to connect the shafts 
of the two machines as before, by clutch or belt ; arrange the eUotriesl 
oonneottcms and instruments as in the following diagram : 




Fto. 7. ' Efficiency test of two similar dynamos. 



D is the dynamo under test ; M is the similar machine used as a motor; 
and G is the generator for supplying current for the losses and differenest 
between M and D. The speed of the combination, as well as the load on D, 
can be adjusted hy raxyiua the field of M. 

The motor, M, drives D bv means of the shaft or belt connection. M geto 
its current f dr power from two sources, yiz. , G and D. In order to detennlDS 
the amount of mechanical power developed by M, and also to be able to 
separate the magnetic and frictional losses in the two machines, a oore4M> 
test should have been made on the machine M at the same speed, eurreol^ 
and E.M.F. as it is to have In the efficiency test. The loss in the cable oon- 
nections between M and D must also be taken into account, and is eaual to 
the difference in Tolts between roltmeters c and 6, X the current nowinl 
in ammeter n. 



Let 



r= E.M.F. of D, shown on c, 
F, r= E.M.F. of M by rm. 6, 
K/y = E.M.F. of G by tbci. a, 

/= amperes current from D by am. n, 
I, = amperes current from G by am. I, 
Iff = amperes current In M = / + A, 

€ = drop in connections between D and M = F— 9^ 
L = loss in connections between D and M r= e X /| 

r = D*8 internal resistance, 
Tx = H*s internal resistance, 

w = core loss -4- armature loss -f- field loss + friction of M is 
watts + L (loss in connections). 



'm 



SLECTRICAL METHOD OF SUPPLYING LOSSES. 389 



Tb 

fr= the Qflefnl output of D = F x A 
Wf =: tnem supplied by O = V„ X //, 
W-\-WiZs. totafenergy sapplled to M, 
ir+ Wf — «r = energy required to drive D, 

nr 

% commercial effloienoy of D = 



JV = electrical loss In D, 
% electrical efficiency rr 



w 



xioo. 



>r + /«r 



XIOO. 



Tbe other way of calculating the efflctenov with this arrangement is to 
yutMaox^ the output = Wy from O, with full load on D. Wx then is the 
kMsas of boUi machines under load ; and knowing the /*A loss In the arma- 
tare and field of each, the efficiency is quickly and accurately calculated. 
Thk method ia best, as no core loss is required, and includes the " load 



Hetk^kl of AopplytniT tlftfi 



Sfct 



Mod^leaHon qf " Kapp Method,'* by Prcf. Wm. L. Pvffertfrofn noiti 
privuLtely printeafor the itudents of the Maseachtuett* Institute 

of Technology, 

0p«clflcatiOB. 

Two similar shunt dynamos under full load, one as a motor driving the 
other as a loaded dynamo through a mechanical coupling. Mains at same 
voltage a» dynamos, and only large enough to supply the full-load losses of 
bomaynamos. 

line up the two dynamos carefully, and mechanically connect them by 
a good form of mechanical coupling, strong enough to transmit the full load 
to the dynamo. 

Connect the field magnet windings of each machine to the supply mains, 
natttoc a suitable fiela rheostat In each. If desirable for any reason, the 
field of the dynamo may be left connected as designed ; but the field of the 
motor, which does not in any way enter as a quantity to be measured during 
the test, should be c<mnected to the supply mains. 




Fio. 8. Diagram of Connections for Professor Puffer's Modifir 
cation of Kapp's Dynamo Test. 

Mtetliod of AtsMrttng*. 

dose the field oirouit of the motor, and by the motor starting rheostat 
gradually bring the motor up to full 8i)eed. The dynamo armature will be 
alio at proper speed and on open circuit. Now close the dynamo field and 
at^ust the field rheostat until the dynanio is at about normal voltage. 
▲4vt t^o speed ronshly at first by the use of the field rheostat of the 
motor, remembering that an added resistance will cause the speed to rise^ 
Next see that the voltage of the dynamo is equal to that of the motor, or, 
ia othn* wordSf that there is no difference of potential between opposite 
sides of the main switch on the dynamo. Close this switch and there may, 
or may not, bo • amaU eurrent in the dynamo armature. Now carefully 



390 TESTS OP DYNAMOS AND MOTORS. 

increase the armature voltage of the dynamo, watching the ammeter^ and 
weaken that of the motor ; a current will flow from the dynamo to the 
motor, and the motor will transmit power mechanically to the dynamo. 

The current which was first taken from the supply wires to run the motor 
and dynamo armatures will increase somewhat. By a careful adjustment 
of the two rheostats and the lead on each machine, the conditions ot f uC 
load of the dynamo may be produced. The motor Is overloaded and Its arm- 
ature will carrr the sum of the dynamo and supplv currents. Great care 
must be taken in adjusting the brushes of the machLaes, because of great 
changes in the armature reactions which take place as the bruahee are 
moved. It is well to remember that a backward lead to the motor brushes 
will increase the speed, as the armature reactions will considerably weaken 
the effective field strength. 

Gautloita. 

The increase of speed will raise the dynamo voltage, and eause the cur- 
rent flowing in the armatures to greatly increase. A forward movement of 
the motor brushes will reduce both speed and current. A forward move- 
ment of the dynamo brushes will increase the armature reaction, and cat 
down the current through the armatures, while a backward movement will 
cause it greatly to increase. Very sreat care must be taken in adjusting 
the brush lead, as a movement oi the brushes of either machine, which 
would be of little importance luually, will produce sometimes a change in 
current value equal to the full-load current. It is quite possible but poor 
practice to produce the load adjustment by use of the brushes alone. 

It is best to have ammeters of proper sise in all circuits, but those actually 
required are in tlxe dynamo leads and in the supply mains. A single volt- 
meter is all that is required. 

The field magnet circuits ought to be connected as shown, and the am- 
meters placed so that the energy in the fields does not come into the test of 
the losses in the armatures. The magnet of the machine under teat, a 
dynamo in this case, should be under the proper electrical conditions for 
the load, yet not in the armature test, because the object of the test can bert 
be made the determination of the stray power loss under the conditions of 
full load ; then having found this, assume the exact values of E, I, and 
speed, and so build up the data for the required efficiency under a desired 
set of oonditions which might not have been exactly produced during the 
test. 

Immediately after the run, all hot resistances should be measured ss 
rapidly and carefully as possible, to avoid smj error due to a change in 
temperature. 

The energy given to the two armatures less the I*R in each armaturSt 
will be the sum of all the armature losses of the two d3rnamoe under the 
conditions of the test, so that we measure directly the armature lo^tes of 
the dynamos while fully loaded. 

It is evident that the two armatures are not under exactly the same 000- 
ditions, except as to speed, for the dynamo armature will have an intensity 

of magnetic field that will give an armature voltage of Vf -f* ^A^A*^^^^ 
the motor will be weaker as F^ is the same for both armatures, and tbe 

motor armature voltage will be Vf — ^A^A» ^^^ the iron core losses wiUba 
made much greater in the dynamo than in the motor. The motor armature 
must carry a current equal to the sum of the dynamo and supply currents, 
and will get much hotter : its reaction will also be greater, and there will be 
a tendency for greater sparking at the brushes. 

The total stray power thus obtained may be divided between the two 
armatures equally, but preferably in proportion to the armature voltages, 
unless the true law for the armatures is known. All resistances of wires, etc, 
must be noted and corrections applied, unless entirely negligible. 

Two 15-H.P. dynamos were tested by the class of '93, usijig this method. 
One of the full-load tests is here given as a sample of calculation. Ths 
exact rating of the dynamos Is not Known, but is nearly 46 amperes at 230 
volts, with the dynamo at a speed of 1600 r.p.m. 



KUSCTBICAL METHOD OF SUPPLYING LOSSES. 391 

The averages of tlie obserred readings taken during the test, and after a 
mn of about fire hours to become heatod, was as below. 



Sxaaaple of Calc«latloa, 

(Connections as shown in Fig. 8.) 

Volts at supply point 220.3 

Amperes ox 16.71 

Output of dTnamo, amperes 46.80 

I>Tnanio field current 1.M6 

Speed 16M. 

To Meature Armature HeHttance. 

Motor F= 1.962 /= 10.18 

Dynamo r= 2.406 7=10.06 

The motCM' field is out of the test while the dynamo field is in the test. 



Calculation. 

Watts supplied 220.3 x 15.71 = 3461. 

Dynamo armature J2. =5 Motor armature Ji» = 

_. 2.406 AM<OT n 1.962 -A.n 

*-=io:08=-^ ^=10l8=-*«^« 

PmtRmd nmm lUm 

U = 45.80 + 1.M = 47.74 7« = 45.80 + 15.71 =. 61.61 

47.74* X .2387 = 56i=PmRmd 61.613 X .1918 = 725.4 = 7*. /2m» 

Dynamo Field = 1.946 X 220.3 = 428.4 

Watts supplied = 3461 

Dynamo field = 428.4 

PR M =i 726.4 

PB D z=i S54.0 

Total heat lost = 16U7.8 1608 

Total stray power = 1763 watts, for both machines. 

47.74 X .2387 = 11.4 + 220.3 61.61 X .1918 = 11.8 + 2203 

= 281.7 =r VmA. = 206JS = r«». 

Diride the total stray power between the two armatures as their arma- 
ture Toltages. 

231.7 
Stray power of dynamo, 231.7 +208.5 ^ *^® ~ ^^' 
Stray power of motor r= 1763 — 028.0 = 835.0. 
The quantity 928.0 is the object of our test, i.e., the stray power when 
is nearly as may be under actual running conditions. 

Calcwlatton of Xfiidond^. 

As run. 

Output of dynamo = 220.3 X 46.80 = 10090 Watts output 

' 664 HRmd 

10090 428 Field 

644 928 Stray power 

428 11990 Watts input to the dynamo. 



11062 = Work done by current. 



392 



TESTS OF DYNAMOS AND MOTORS. 



Effloienoj of GonTenlon: 

11002 X 100 



11990 



= 92.2 per cent. 



Gommerolal eiBoienoy; 



10090 X 100 
119.90 



r= 84.1 per cent. 



=: 16.1 H.P. 



Power required to run dynamo: 

11990 
746 

In this test, carbon bruahes were used, and the lead adjuBtod afe carefvUt 
AS possible, if the exact rating of this dynamo had been 46 amperes and S20 
▼olts at a speed of 1000. and we wished to find the efllolencies corresponding, 
we should proceed In this way. 

The test was made under conditions as nearly as possible to the railng, 
and the stray power as found will not be perceptibly different from what It 
would be under the exact conditions. 

When the load has been as carefully adjusted as in this test, It Is seldom 
worth while to make these corrections, as they are smaller than ehaoffes pro- 
duced by accidental changes of oiling, temperature, brush pressure, eCe,, 
of two separate tests. 



itac«a of tta« Metfewd. 

Small amount of energy used in making the test, namely, only the losses. 
No wire or water rheostat required. Test made under full load, and yet 
the losses are directly measured. AH quantities are expressed In terms de- 
pending on the same standards, and therefore the efflcienovwill be but little 
affected by any error In the standards. No mechanical power messure- 
ments are mikie, and all measurements are electrical. 



Bequires two similar machines. Armature reactions are not alike In both 
machines. Leads are not alike. The iron losses are not the same. No belt 
pull on bearings. Must line up machines and use a good form of mechanical 
coupling. Sometimes difficult to set the brushes on the motor. The motor 
armature is much OTorloaded. 



RH. 





RK. 

scpar9<te exciter 
for fields 
of motors 



FlO. 9. Diagram of Connections for Test of Street 
Motors, Prof. Puffer. 



Gar 



ELECTRICAL METHOD OF SUPPLYING LOSSES. 393 



(LflA 



FIKLO 




Fio. la Diagram of Connections of ModUoation of the 
Preylona Diagram, by Prof. Puffer. 

lUs melhod Is of advantage In the test of railway seriee motors, If slightly 
modified bj the separate ezoitation of the motor fields. If the series field 
vliidlna be not separately excited there will be a great deal of nnneces- 
nry difflcolty from great changes of speed as the load is raried. HoweTer. 
one field may be kept in circuit on the machine used as a motor, as ihe test 
esn then be made with the motor under its exact conditions. There will be 
a rery great change of speed during adjustment of load, but there will be no 
dssfer of injurinflr anything, as the separate excitation of the dvnamo field 
is an aid to steaolness. lutilway motors, as generally made, iRill not stand 
tfaslrfnll rated load continuously, and tne motor is likely to get too hot if 
not watched ; the machine Ufted as a dynamo will run cold, as it will not 
have a large current in it. The friction of brushes is very large In these 
BMitors, and in general there is a want of accuracy In the diyision of the 
total stray power between the two armatures. It can only be very approxi- 
mately done by the aid of curves showing the relation between speed and 
stray power, and armature voltage and stray power. 

IftyMmaem's K«et of two Siaillmr I^lroct-CTmrromt Pymmmioe. 

In the original Hopkinson method, the two dynamos to be tested were 
placed on a common foundation with their shafts in line, and coupled to- 
gether. The combination was then driven by a belt from an engine, or other 
source of power, to a pnlley on the dynamo shafts. The leads of both ma- 
chines were then Joined in series, and the fields adjusted so that one acted 
as a motor driven by current ftom the other. The ot^ide power in that 
esse sni^lied, and was a measure of the total loesea in tne combination, the 
efficiency of either machine being taken as the square root of the efficiency 
of the combination. 

Many modifications of this test have been used, especially in the substitu- 
tion of some method of electrically driving the combination, as the driving- 
power is so much easier measured if electncal. 

This test is somewhat like that last given, but the two machines are con- 
nected in ssHes through the source of supply for the dWerence in power, 
soeh as a storage battery or generator. The following cuagram shows the 
eonneetions for the Hopkinson test, with a generator tor supplying the dif- 
ference in power. 

In this test the output of G plus enezgy taken by M| (motor driving the 
system), gives losses of motor and dynamo (the losses of M, being taken 
out), lliese losses being known, the efficiency can be calculated. 

If the two machines D and M are alike, O supplies the i^^ losses of arma^ 
tores, and M the friction, core losses, and /> Rot fields. 

Another method useful where load and current are both available, is to 
drive one of two similar dynamos at a motor, and belt the second dynamo 
to it. Put the proper load on the dynamo, and the efficiency of the com- 
Unation is the ratio of the watts taken out of the dynamo to the watts 
sumllsd to the motor. The efficiency of either machine, neglecting small 
dineienees, is then the square root of the efficiency of both. 



r 



394 



TESTS OP DYNAMOS AND MOTORS. 



A.M.I 




Fia. 11. 



Diagram of connections for Hopklnson'8 test of 
two similar dynamos. 



If 






watts put into the motor, 

watts taken from the dynamo, 

per cent efficiency of the combination, 

efficiency of either machine, 

Px XlOO 



The above test is especially applicable to rotary converten, the belt being 
discarded, and the a e sides bmng connected by wires ; thus the first ma* 
chine supplies alternating current to the second, which acts as a motor 

generator with an output of direct current. The only error (usually small) 
I due to the fact that both machines are not running same load, since that 
one supplies the losses of both. 

Fleaslar'a ModMlcatloa of HfovblMaoB T««t. — In this ease ths 
two dynamos under test are connected together by belt or shafts, and ars 



A.M.nr 



7 




7 
I 



FlO. 12. 

driven electrically by an external source of current, say astorace battery or 
another dynamo, which is connected in series with the circuit of the two 
machines. Figure 12 shows the connections for this test, which will be found 
carried out in full in Fleming's '* Electrical Laboratory Notes and Forms." 

Motor Teste. 

Probably the most common method of testing the efficiency and capA> 
city of motors is with the prony brake, althougn in factories where spars 
dynamos are to be had, with load ayailable for them, there can be so 



MOTOR TESTS. 396 

qMBtion Uiat b«lUiig the motor to the dynamo -with an electrical load ia 

by far the moet accurate, and 

L I t the easiest to carry oot. 

t t f » briA* teat. — In 




this test a pulley of suitable 
dimensions is applied to the 
motor-shaft, and some form of 
friction brake is applied to the 
puUcT to absorb the power. 

The following diagram shows 

v«>j 13 one of the simplest forms of 

prony brake ; but ropes, straps, 

and other appliances are also often used in place of the wooden brake shoes 

u shown. 

NoTB. — See Flather, ** l>fnamometer» and the Meamrement of power," 

As the friction ot the brake creates a great amount of heat, some method 
of keeping the pulley cool is necessary if the tost is to continue any length 
of time. A palleT with deep inside flanges is often used ; wator is poured 
foto the pulley after it has reached its full speed, and will stay there by 
resson of the centrifuiral force until It is eyaporated by the heat, or the 
speed is lowered enough to let It drop out. Rope bralces with spring bal- 
ances are quito handy forms. 

Tlie work done on the brake per m inuto is the product of the following items: 

I = the distance from the centre of the brake pulley to the point 

of bearins on the scales, in feet. 
n = number ofrevolutions of the pulley per second, 
w = weight in lbs. of brake bearing on scales. 
Power = 2 V inir = foot-pounds per second, and 
wv _ 2*lntD 
^•^— 560 
Tbe input to the motor is measured in watts, and can be reduced to horse- 
power by diTiding the watts by 746 ; or the power absorbed by the brake 
esD be reduced to watts as follows : — 

If the length, /, be given iu centimeters, and the weight, 10, be taken in 
grams, the power absorbed by the brake is measured directly in 
ergs, and as one watt = 10' ergs, the 

Watts output at the brake = —.57 — = -P- 

p 
The watts input = Pt and ei&ciency in percentage = ^ X 100. 

If the output is measured inlzs: feet and fo=z lbs., then 

P = 2.72»Iir. 

Pi 
Input in horsepower = ^^i 

2irlniff . 
Output in horsepower = — and 

BAciency in percentage = 100 . A^. 

If it is desired to know the friction and other losses in the motor, after the 
brake test has been made, the brake can be removed, and the watts neces- 
•sry to drive the motor at the same speed as when loaded, can be ascertained. 

Clsictrlcal l««d Uittiincluding loss in belting, and extra loss in bear- 
ings due to puU o/beli).— This test consists in belting a generator to the 
motor and measuring the electrical output of the generator, which added to 
the friction and other losses in the generator, makes up the load on the 
motor. The efflciency is then measured as before, bv the ratio of output to 
input. The great advantage of this form of test is, tnat it can be carried on 
for any length of time without trouble from heat, and the extra loss in 
bearings due to pull of belt is included, which is therefore an actual com- 
mercial condition. 




I 

396 TESTS OF DYNAMOS AND MOTORS. 

In thto form ol test the losset in the generator are termed eomnier torque, 
and the method of determining them is given following this. 

CoMBter torq««t— In tests of some motors, espeicially indnotlon mo- 
tors, the load is supplied by belting the motor under test to a direet current 
generator hairing a capacity of output sufficient to supply all load, inclndiqg 
orerload. 

In determining the load applied to the motor and the counter torgme, it is 
necessary to know, besides tne /. S, or watts output of the generator, tlie 
following : ~ 

T^R of generator armature. 

Core loss of generator armature, 

Bearing and orush friction and windage of gonerator^ 

Extra bearing friction due to belt tension. 



It is necessary to know the above items for all speeds at wbloh the 
bination may have been run during the testing. This Is especially useful 
in determining the breakdown point on induction and synchronous motors, 
both of which can be loaded to such a point that thev ** fall out of step.** 

While the motor is under test especial note should oe made of the speeds 
at which the motor armature and generator armature rotate, and of the 
watts necessary to drive the motor at the various speeds without load. 

The eownter torque will then be the sum of the following three items : — 

P = i* J2 of generator armature, 
p0 =: core loss of generator armature, 
J^= bearing and ornsh friction and windage of the generator armature. 

The field of the dynamo must be separately excited and kept at the same 
value during the load tests and the tests for " etrap po»er,*'^ and does not 
enter into any of these calculations. 

JBclt-on tmmt, — After dlsconneotinff current from the motor under 
test, and with the belt or other connection still in place, aupplv sufficient 
voltage to the dynamo armature to drive it as a motor at the speeds 
run during the motor test, holding the field excitation to the same value as 
before, but adjusting the voltage supplied to the armature for changing the 
BDeed 

Take readings of 

Speed, i.e,, number of revolutions of dynamo armature, 
volts at dynamo armature. 
Amperes at dynamo armature. 

Oonstruct a curve of the power required to Mre the eomblnation at the 
various speeds shown during the motor test. 

Relt-oir teat. —Throw the belt or other connection off, and take read- 
ings similar to those mentioned above, which will show the power neoeesary 
to drive the dynamo without belt. ^ ^ 

Then for any speed of the combination the " itray power** will be found 
as follows : — 

P, = watts from helt-of curve, required to drive the dynamo as a motor. 
P„ = watts from lelt-^m curve, required to drive the combination. 
P« =r core loss in dynamo armature. 

^ = friction of dynamo ftel<-e>^. ,. , - ...^ ^ ,. 

F, = friction of motor under test, running light and without belt. 

y''= Increase In bearing friction of dynamo, due to belt tension. 
f-zz increase in bearing friction of motor, due to belt tension. 

From the 6eW-o^ curve, 

P.zzPc + F 0) 

From the beltrcn curve, 

P„:=P, + F'\-F,+/+/, A 



INDUCTION MOTORS. 



397 



Ssbtraet (1) item (2) 



P,,'-P. = F,'^/+A 



(3) 



Tlie Talnet of / and A eannot be determined aeonntely : but If the ma- 
ehinM are of aooat the same sise aa to bearings and weights of morlng 
parts, it is Tery close to eall them of equal ralue, when, 



/ or/^ = ^ 



(4) 



The friction F, of the motor under test has been prerionsly found by 
Bocfng the watts necessary to drire it at the various speeds. If it is an iii- 
iiacHen motor, the Impressed voltage is reduced very low in determining 
ttM friction in order that the core loss may be approximately aero. 

As sll the Talnes of the quantities on the right-hand side of the equation 
(^ are now known,/ is determined, and may be added to P^ to give the total 
"tlnui power.** A curre is then plotted from the ralues of ** $tray power ' 
at diiferent apeeds. 

■ 

Qmmier torque = (P, +/). 

Total had=i IJB + PR+ (^/ +A 
vbare IJS = watts load on the D. C. machine when it is being driren by 
tha motor. 



tba motor. 
US=:P, +/= " stray power,*' 
Total load = /JP + /*ii + '9. 



then 



TkeTalueof/is so small when compared with the total load, that any 
■itaary error in its determination will be unimportant. 



VMt of MU 'm^UWkmtHwrmj Hotova. 

Tha **pmHping-baie1k *' test, as described before, with some little modiftca- 
tkm aenres for iesting street-railway motors. The following diagram shows 
tba arrangement and electrical connections. 

The motora are driren mechanically by another motor, the input to which 
k a meaaure of the 
loiMa, frictional, oore 
loMea, sears, bearings, 
ate., in the two motors ; 
tlis two motors are 
Mueeted in series, 
ttroqrii a booster, B, 
cira Deing taken to 
nuke the connections 
In luch a manner as to 
bare the direction of 
rotation the aame ; 
and their voltages op- 
POriag 




SUPPLYING CORE 
L088E8 AMD Fmcmi 




8UPPLYINQ 



VM. 



Fici. 14. Diagram of connections and 
ment of street-railway motors. 



arrange- 



AflMlnies are taken and the efficiencies are calculated as in the " pumping- 
WFtSt. 

In eliminating the friction of bearinffs, etc., and of the driving-motor, it is 
'Ui ftrat without belts, the input being recorded as taken, at the speed 
itoceiBary. The belt is then put on and a reading taken at proper speed, 
vlth beta the motors under load. 

The load being adjusted by varying the field of booster B, the total losses 
otttie ayatem are then IB from booater plus the difference between belt-on 
'Mding with full load through the motors, and belt-off reading as noted 
(allowance being made for onange of I*R of driving-motor). If the two 
motors are similar, half this value is the loss in one motor, from which the 
sfBdeney oan be calculated as previously shown. 

* ~ — In addition to the tests to which the D. G. motor 



398 TESTS OP DYNAMOS AND MOTORS. 

b oixUnarily submitted, there are seyeral others usually applied to the in- 
duction motor, as follows : — 

ExciUUUm; Stationary impedance ; MaxUMun output; and some Tarlations 
on the usual heat and emoiency tests. 

Excitation: This is also the test foroore loss^- friction, allowaiie« beioff 
made for / *R of field ; with no belt on the pulley the motor is run at f nfi 
impressed voltage. Kead the amperes of current in each leg, and total 
watts input. The amperes give the excitation or " running-light*' oorrent, 
and the watts g^ve core loss + friction -f- /'J7 of excitation current. 

Stationary impedance: Block the rotor so it cannot move, and read volts 
and amperes in each leg, and total watts input. This is usually done at 
half voltage or less, and the current at full voltage is then computed by 
proportion. This then gives the current at instant of starting, and a meas- 
ure of impedance from which, knowing the resistance and core loss, other 
data can oe calculated, such as maximum output, efficiency, etc. 

Maximvan output: TnU might be called a orecuc-down test; as it merely 
consists in loaiung the motor to a point where the maximum torque point is 
passed and thus the motor comes to rest. 

Keep the impressed voltage constant and apply load, reading volts, am- 
peres In each leg, the total watts input, and revolutions ; also record the 
load applied at the time of taking the input. Then take countet: torque as 
explained before, from which the efficiency, the apparent efficiency, the 
power factor, and maximum output are immediately calculated. 

IIe»t t«a*.— Bun motor at full load for a sufficient length of time to 
develop full temperature, then take temperatures by thermometer at the 
following points : — 

1. Room, not nearer to the motor than three feet and on each side of motor. 

2. Surface of field laminations. 

3. Ducts (field). 

4. Field or stator conductors, through hole in shield. 
6. Surface of rotor. 

6. Rotor spider and laminations. 

7. Bearings, in oil. 

During heat run, read unperes and volts in each line. 

IMcteiicy t«at. — Apply load to the motor, starting with nothing birt 
friction ; maxe readings at twelve or more intervals, from no load to break- 
down point. Keep the speed of A. C. generator constant, also the impressed 
voltage at the motor. 

Bead, Speed of motor. 

Speed of A. G. dynamo. 

Amperes input to motor, in each leg. 

Volts impressed at motor terminals. 

Watts input to motor, by wattmeter. 

Current and volts output from D. G. machine belted to motor. 

Counter torque as explained above, and excitation reading watts. 

From the above the efficiency, apparent efficiency, power factor 

— P*^ -^~ ? ) , and maximum output can be calculated. 

real efficiency / 

In reading watts in three-phase motors, it is best to use two wattmeters, 
connected as shown in following sketch : — 

1, 2, 3, are the three-phase lines leading to the 
motor. 

A and B are two wattmeters. 

6 is the current ooil of A, and h^ of B. 

a is voltage coil of A, and a^ of B. 

The sum of the deflections of A and B give total 
watts input. At light loads one wattmeter usually 
reads negative, and the difference is the total watts. 

Resolts* — At the end of the preceding tests the 
following results should be computed, and curves 
plotted mm them. 

^ « % synchronism = ^55*^B2*2I21i??- 

Fig. 15. ' Synchronous speed. 



( 




"^ 



BYNCHBONOU8 HOTOR. 



Tarqa»fWDiid> poll at 1 n. radln* = 

- iboTB r««QltB 

n tnm Stelnmai 



ee gliDlUr to Fig. le, 



Tia. IS. CtuVH of rwultiottnta of Induction motor. 

■7wkr*B««B H*tar. — Synchronoiu moton ^re senaratelT eiclted, 
"olUaD.C. exciter ihould hme Its qu»lLtI« tostert u a djnamo. Bjn- 
'"MOMmotorBsretffliledforflrrai-iJoimpoinf,- Starting Burr«iiBt dlffer- 
W polali of locatioR of th« ntor ; Lrait rxciUnn carrenltor T&rtoug lowls. 
AU Ukh Id Bddillon to the regulitr emciencT and other testa. Core loHei, 
™a<. />JI loHea. etc.. can be foond by any of the usnal methods pre- 
"OMlT dwertbed. 

Bnatdmm point. SjnehrnnoiiB molore have but little etartlng-lorquo ; 
™ " li n9««ftry to rtart them without load, throwing It on gradaally 
«Biii.motorhMMittled>te»dlly and irlthonf hunting'- on lu lynehro- 
""■ ipBHl. The bresk-Jown point Ii found by applylna loud to the point 
■bnihemotor fall! outor>tep. which nil! be Indlnaled by a violent rash 
«nrnnl Id Che ammeter simultaneous witb the I'luving dovrn. 

TUtlsPtlsusnaUy carried out at abonl half vnltage.fiie ratio of the load 
°;a|eniotor»t the moment of dropplnr out of Ble|, will be to the full load 
« htak-down aa Ihe square of the vollngcs, the load being adlualed at 
"otaiim Input In each case. For eiample. say a certain motor, built to 
"""WOO Tolta, breaks down at IBO K.W.. with an impraued Toltue of 
Wn. Tlienllu true foil brea)t.dowii load will b« 



i 



i.oon' _ 



K.W. 



Dai 

flel 



400 TESTS, ETC. 

Starting ewrrent. Owing to ooiueqaent dbturbanoe to the line, tt Is dani- 
rable that the starting current of a sTnchronoos motor be out down to the 
lowest point ; but it is difficult to reduce this starting current lower tbaa 
200% off ull-load current. A synchronous motor also starts easier at certain 
positions of its rotor as related to poles. With the rotor at rest, and the 
location of the centre of its pole-pieces chalked on the opposite member, 
the circuit is closed, the impressed voltage Is kept constant, and the current 
flowing in each leg of the circuit is read, and the time to reach synchro- 
nism. Care should be taken to note the amount of ttkeftrstrush of current, 
and then the settling current at speed. 

Lecut exciting eurrent. The power factor of a synchronoiis motor will be 
100 only when, with a given load on the motor, the exciting current is ad- 
justed so that there is neither a leading nor lagging current m the armature. 
Sometimes It is desirable to produce a leading current In order to halawe 
the effect of induction motors on the line, or inductance of the line itself. 
This is done by over-exciting the fields. 

With fL given load on the motor, the 100 power-factor is found by coin- 

aring the amperes in the motor armature with the exciting current in the 
_eld. Starting with the excitation rather low, the armature current will be 
high and laggmg ; as the excitation is increased, the armature eurrent will 
drop, until ft reaches a point where, as the excitation is still increased, the 
armature current begins to rise, and keeps on rising as the exciting current 
is increased, and on this side of the low point the armature current is 
letiding. 

With no reason for making a leading current, the best point to run the 
motor at is, of course, that at which the armature current Is the lowest ; and 
at that point the power-factor is 100. 

SrncliroMom Insp«d»ac«.— The EJBC.F. of an altematixig dynamo 
is the resultant of two factors, i.e., the energy E.M.F. and inductive E^Ji.F. 

The energy E.M.F. may be determined from the saturation curve by run- 
ning the machine without load, and learning the field strength necessary to 
produce full voltage. 

The inductive E.M.F. is at riffht angles to the energy B.M.F., and Is de- 
termined by driving the machine at speed, short-circuiting the armature 
through an ammeter, and exciting the field just enough to produee full-load 
current in the armature. The amount of field current necessary to produee 
full load is a measure of the ifufuclire E.M.F., which can be determined ftom 
the saturation curve as before, and the resultant E.M.F, will be 

Besultant E.M.F. = Venergy E.M.F.* -{■ inductive E.M.F.*. 

•tttvratloa teat.— This test shows the quality of the magnetic <Ar^ 
cult of a dynamo, and especially the amount of current necessary to saturate 
the field cores and yokes to a proper intensity. In this test it is Important 
that the brushes and commutator be in good condition, and that all oontaets 
and joints be mechanically and electrically tight. 

The dynamo armature must be driven at a constant speed, and the leads 
from the voltmeter placed to get readings from the brushes of tixe dynamo 
must have the best of contacts. 

The fields of the dynamo must be separately excited, and most have in 
the circuit with them an ammeter and rheostat capable of adjusting the 
field current for rather small changes of charge. 

The armature must be without load, and a voltmeter must be connected 
across its terminals. 

Should there be residual magnetlBm enough In the iron to produce any 
pressure without supplying any exciting current, such pressure should be 
recorded ; or perhaps a better way is to start at zero voltage by entirely 
demagnetizing the fields by momentary reversal of the exciting current. 

To start the test, read the pressure, due to residual magnetbm if not de- 
magnetized, or if demagnetized, start at zero. Give the fields a small ex- 
citing current, and read the voltage at the armature terminals ; at the same 
time read the current in the fields, and the revolutions of the armature. 
Increase the excitation in small steps until the figures show that the knee of 
the iron curve has been passed by several points ; then reverse the operation, 
decreasing the excitation by like amounts of current, until zero potential is 
reached. 

This is usually as far as it Is necessary to go in practice ; but occasionally 



^ 



RB8ISTANCE OF ARMATURE. 401 

It li well to oompleta the entira magnetio eyele by Mrenlng tho ez«itiBgeiii^ 
not, and lepeaong the steps and readings as abore described. 

The readings should be plotted in a cnrre with the amperes of ezeitiag 
eurrent as abedasae, and rolts pressure as ordinates. 

The E.M.F. will be found to inerease rapidly at first; and this increase 
vill benearlT proportional to the exciting current until the ** knee ** in the 
enrre is reached, when the E.M.F. increase will not be proportional to the 
excitation until after the ** Jntee" is passed, when the increase in E.M.F. 
vill again become nearly proportional to the excitation, but the increase 
will be at such a low rate as to show that the magnetic circuit is practically 
ntnrated ; and it is not economical to work the iron of a magnetic circuit too 
fir aboTe the knee, nor is it expedient to work it at a point much below the 
"faiee,'* except for boosters. 

The excitinig current must not be broken during this test, except possibly 
at lero ; nor must its Talue be reduced or recededf rom in case a step should 
be made longer than intended. Inequalities of interval in steps of excit- 
iBf eorrent will make little difference when all are plotted on a enrye. For 
tke same Talue of exciting current the down readings of E.M.F. will always 
be Ugher than those on the up curve. 

MmaUimm^m of fleUI coils.— The resistance of the shunt fields of a 
dynamo or motor can be taken in any of the usual ways : by Wheatstone 
bridge ; by the current fiowing and drop of potential across the field termi- 
Bals ; and it is usual, in addition, to take the drop across the rheostat at the 
now time. The resistanoe of each field coil should be taken to insure that 
•U are alike. 

Besistanee of series fields, and shunts to the same, must be taken by adif- 
faent method, aa the resistance is so low that the condition of contacts may 
vary the results more than the entire resistance required. The test for re- 
riitekoe of armatures following this is quite applicable. Of course any test 
for low resistances is applloable ; but the one described is as simple as any, 
•ad quite accurate enough for the purpose. 

Mesistaaca •€ »msatnre. — In order to determine the I*R loss in a 
ffBaerator or motor armature, its resistance must be measured with oonslder- 
aUe eare ; and the ordinary Wheatstone bridge method is of no use, for the 
nsson that the Tarlable resistance of the contacts is often more than that 
of the armature itself. The dr(^ 
■Mthod, so useful with higher re- 
tltitiaee derices. Is not accurate 
caoBf^ for the work ; and the storaqe . 
nost accurate method Is probably battery : 
Uiedirect comparison with a stan- 
dard resistance by means of a AojurrASLEi 
pod ga lTanometer and a storage RESiSTANCi \ 

Clean the brushes, commutator resistanoi 

Rirfaee, or surface of the col- a 

)eetor>rittgB, and in the case of a 

D. C. machine, see that opposite FlO. 17. Diagram of arrangement for 
brushes bear on opposite seg- measuring resistance of armatures. 
Bents. 

Connect tbe galvanometer and Its leads, the storage battery and resis- 
taaeee, ss in the following diagram. The standard resistance, R, will ordina- 
rily be about .01 ohm, but may be made of any size to suit the circumstances. 
Toe storage battery must be large enough to furnish practicallv constant 
current during the time of testing. The galvanometer must be able to 
■tand the potentials from the battery ; and it is usually better to connect in 
Mries with it a high resistauce, so that its deflections may not be too high. 
The deflection of the galvanometer should be as large as possible, and pro^ 
portional to the current flowing. The leads a, a,, and b and &i, are so ar- 
laased with the transfer switch that one pair after the other can be thrown 
in (nrcuit with the galvanometer ; and it is always well to take a deflection 
lint with B, tiien again after taking a deflection from the armature. 

The leada a and Oj must be pressed on the commutator directly at the 
bnish coataeta, and may often oe kept in place by one of a set of brushes 
at either side. 

Test.— Close the switch, k^ and adjust the resistance, r, until the am- 
meter shows the amount of current deured, and watch it long enough to be 





402 



TESTS, ETC. 



rare it is oontteat. Oloae the transfer switeh on b and 6|, and read fhe fil- 
▼anometer deflection, oalling it d. Throw the transfer switch to the eo»> 
tacts a, and a,, read the gaWanometer deflection, and call it d,. Transter 
the contacts back to b, and fr| and take another reading ; and if it diffen 
from di, take the mean of the two. 

Let X = resistance of the armature, then 

*= B^. 
a 

NoTB. — See Fleming*s ** Electrical Laboratory Notes and FomiB.'* 



Teats for Faulta la Amata 




STonoEnxrrrcw 



The arrangement of galvanometer for testing the resistance of an armap 
tnre is Uie very best for searching for faults in the same, although it is not 
often necessary to measure resistance. 

T«tst for opciB circBlt. — Clean the brushes and oommutator, then 
apply current from some outside source, say a few cells of storage battery 

or low pressure dynamo, through an am- 
meter as in the following diagrams. Note 
the current indicated in the ammeter; ro- 
tate the armature slowly by hand, and if the 
break is in a lead, the flow of current will 
stop when one brush bears on the segment 
in fault. Note that the brushes must not 
cover more than a single segment. 

If on rotating the armature completely 
around the deflection of the ammeter does 
not indicate a broken lead, then touch tiie ter- 
Fio. 18. Test for break in ar- ?»n*^» <>' t^« galvanometer to two adjaoent 
mature lead. hunt working from bar to bar. The defleo- 

tton between any two oommutator bars 
should be substantially the same in a perfect armature ; if the deflection 
suddenly rises between two bars it is indicative of a high resistance In the 
coil or a break (open circuit). 

The following diagram shows the oonne^y 
tions. 

A telephone receiver may be used in place 
of the galvanometer, and the presence of 
current will be indicated by a " tick '* in tha 
instrument as circuit is made or broken. 

Toat for abort circuit. — Where two 
adjacent commutator bars are in contact, or 
a coil between two segments becomes short- 
circuited, the bar to bar test with galvanom- 
eter will detect the fault by showing no 
deflection. If a telephone is used, it will be 
silent when its terminal leads are connected 
with the two segments in contact. See dia- 
gram below for connections. If there be a short circuit between two coils 

the galvanometer terminals 
should include or straddle three 
commutator bars. The normal 
deflection will then be twice that 
indicated between two segments 
until the coils in fault are 
reached, when the deflection will 
drop. When this happens, test 
eacn coil for trouble ; and if indi- 
vidually they are all right, the 
trouble is between the two. The 
following diagram shows the con- 
nections. 

tvro. — Place one terminal of the 
galvanometer on the shaft or 




Fio. 18. Bar to bar test for 
open circuit in coiL 




SHORT coMurr 

BETWEEN SEQMENTfl 
OR IN OOIL 



.StMAOa ■HUMT ** 

^TTEBY 

9n. 20. Bar to bar test for short eir- 
enit in one coil or between commuta- 
tator segments. 



frame of the machine, and the other terminal on the commutator. (Ihm 



ARMATURE FAULTS. 



403 



9agt battery, ammeter, md leads most be thorotghly insulated from 
mL) If, DUDder these ctronmBtancee, there is any deflection of the gal> 
pNseter, it indicates the presence 





.** STOfUdC 



Shimj 



Fig. 21 . Alternate bar test for short 
circuit between sections. 



p fmuuf , or contact between the 
Imre ooaductors and the frame 
ifte machine. More the terminal 
Mt the eommntator until the least 
pKtioa is shown, and at or near 
liinist will be found the contact 
[lie particular eoil connected be- 
ns two segments showing equal 
■e ti an^ unless the contact happens 
dose to one segment, in wnich 
will be aero deflection. 
^ ID field coils can be located 
method. The following 
I riiowB the connections. 

tfarmatitre qf nmUipolar dynamo U electricallp centred, put 

down brushes 1 and 2, and take rolt- 
age of machine ; put down brush 3, 
and lift 1, take voltaae again ; put 
down brush 4 and lift 2, again tak- 
ing yoltaee; repeat the operation 
with all the brushes, and tne volt- 
age with any pair should be the 
same as that of anv other pair if the 
armature is electrically central. 

The same thing can also be deter- 
mined by taking the pressure curves 
all around the commutator as shown 
in the notes on characteritUei on 
dynamos. 



T«8t for ground in armature 
coils. 



As tbore the brushes should be exactly at the neutral point. 




( 



ALTERNATINGh-CUBBENT MACHINES. 

RaviasD bt E. B. Raymond and Cbcil P. Pools. 

Fob altematlxig or periodically yarying oorrents there are three Talon at 

the E.M.F. used, or of which the ralue is required : 

a. The maximum value, or the top of the urare. 
6. The instantaneous value o f a poi nt in the wave. 

c. The effective E.M.F., or Vmean* value of the full wave. 

Since the maximum value of a sine curve = | x its average value, the 

maximum value of the E.M.F. of a single-phase hi-polar alternator pro> 
ducing an alternating sine waye of E.M.F. Is 

_ V • jy^ 2 r.p.s. ^^^^ w* Ift r.p.8. 10^ 

2 q q 

In an alternator having p poles and m phases, 

w Jfc ♦ N9P r.p.s. IIP* 



2 mq 

where X; is a number ranging from 1 to 2.5, depending upon the shap^ of the 
coil of the armature ana al«> upon the shape of the pole-piece. iv« = nnm* 
her of conductors ; q == number of paralleT paths in each winding or phase 1 
The instantaneous B.M.F. in one winding at any moment 

- ' V ^'«Xr.p.s. x»XPX*i<r< . 
-gX — ^ Xsinf, 

where 9 = the angle through which the armature has turned from the posi- 
tion where the coil embraces the maximum flux. The most important value 
of all is the square root of the mean square value of the sine wave of KMJF^ 
since this value is the effective or working value. It is equal to the maxi- 
mum value of a sine E.M.F. wave -f- V2, 
Hence 

_ w *»^«p r.p.s. 10-« l.llh*jrtpT.pjk.Vr* 

2 V2 mq mq 

In lAree-^Aoss alternators the E JIC.F. between terminals will depend upon 
the method of connecting the armature conductors. The two most common 
methods are called the delta connection and the Y or star connection, both 
shown in the following diagrams. 





DELTA OONNECTMMI Y OR STAN OONNECTIOII 

Flos. 1 and 2. Values of E.H.F. in three-phase connections when x =: y = s. 

In the delta-connected armature the E.M.F.'s between terminals are those 
generated in each coil, as shown in the diagram. 
In the Y-connected armature the E.M.F. between any two terminals is 

the E.M.F. generated by one of the coils in that phase multiplied by the Vi 
or 1.732. 

Two-phase circuits are sometimes connected as a three-phase circuit ; that 
is, both phases have a common return wire. In this case the pressure be- 
tween the two outgoing wires is V2 x E^ and the current in the oomraca 

return will be / V2, both conditions are on the assumption that E and / hi 
each phase is the same. 

404 



ENERGY IN THREE-PHASE CIRCUITS. 



405 



kolst 



bcsmat from an alternator depends npon inductance and reeietance. 
reoeSeient oC inductance 1b represented by the letter L. The B.M.F. 
. alternator follows approximatelr a sine curve, and the cnrrent from 
>y the same kind or curre. Since in a circuit, lines of 
in proportion to the current flowing, at each of its different our- 
tnere is a new value of lines in force. Thus, in a circuit of 
J current there is a continuously raryiug flux, and hence there is in- 
1 a back £^.F. This back B.M.F. is called the back E.M.F. of self- 
. and it retards the current flow Just as does resistance, 
back £J(LF. of self-induction combines with the reBistaiioe» but at 
lassies thereto, the result being called impedance. 

tsodBciant of self-induction =r 

msiC. flux X t«rn« ^ ».«««„ 
^ = amperes XIO* -^"^^^^ 

I multiplied by 2 v / = reactance ohms (/= cjcles per seoond). 
a cireuit where R = resistance ohms, ana 2 n fL = reactance ohms. 
MBbiiie at right angles to produce impedance ohms, or the total 
foree of the current, thus: 

Impedanoe = Vjp-4-(2»/Z)2. 

b an alternator circuit if the coefilcient of self-induction of the 

be X, and that of the external circuit be £, ; and If the resistance 

sltemator armature be J2, and that of the external circuit be ^ti 

eSeetiTe E.M.F. generated in the alternator armature =: J?, then 

flowing will be 



itir«lj' ]f«M-Iad«ctlre aaiA 1 
Three«Pliaii« Otrcolt. 

.•.Mknrtm, dl.c»m of . TH«mn«rt«l m-ltiphMO ^n,r.tor and olr- 

Cj =r E.M.F. of any phase in the armature, 
i, =: current of any phase in the armature, 
B = E.M.F. between mains, 
/ = curroit In any main, 





Fig. 3. 

Py = power of one phase of the armatursi 
P =r total power, 

P = 8 »t = ^^= 1.732 EI, 



/= 



1.732 ir 



.406 



ALTERNATING-CURRENT MACHINES. 



In the following diagram of a delta-conneoted polyphase generator 
eirooits, let 

/> = 3P, = ?J^ = 1.782 JP/, 



1.732 f 




Fio. 4. 



Where the olronit is indactive, in order to determine the teal power the 
above result must be multiplied by the " power factor.*' or theoosine of Uwj 
** angle'* by which the current lags behind or leads the E.M.F. Thus tw 
power in a circuit in which the current lam 9 degrees behind the E.M.Fr^ 
IE cos 9. If the current lags W^ behind the E.M.F. there will be no energf 
developed as cos 90^ = 0. { 

The cosine of the angle of lag «, or the power factor, is equal to the ratii^ 
of the true watts to the apparent watts. In ordinary lighting dlstributioafel 
the power factoi* is high so that rough calculations are made without Hij 
▼alue being exactly known. 

Aarl* of Iifici V« AeteraslMe with a watt aseter ta tlm**^ 
pluwe drcaita (Fig. 6) : Connect the current ooU in one lead ; oomwtt; 



Wm 




Fio. S. 

one end of the potential ooil to a; on the same lead ; now eonneet the r^ 
maining end first to one of the remaining leads y , then to s, calling the fint 
reading Pj and the second, Pjj ; then if 9 = angle of lag, 

When 9 is greater than 60 degrees, one reading will be negative, so tbst 
the difference of readings will to greater than their sum. 

If JR= resistance per leg of T-connected armature, 

r= resistance per phase of A-connected armature, 
then, 

PR loss in Y-connected armature =8 l^R 

I^R loss in A-connected armature = 3 (tt^V = Pr. 

CHrcaifa. 



■aerfy ta Hoa«ladactlTe Vlirea- 

/ =■ current in any one of the three wires of external circuit, 
« = current in one phase of the armature for delta connection, 
7>= watts output oi a balanced three-phase generator, 

1.732= VJ, 
.STTzzl-i-Va, 
£=Tolts between terminals (or lines) on either delta or Y svstem, 
v = volts of one phase of the armature if connected in ** Y,*' 
22= resistance per leg, of Y-connected armature, 
r= resistance per phase of A-connected armature, 

P^Z /, © = ^-^jz^-^r B 1.732 (either with Y or A armature). 



COPPEK LOSS IN ARMATURES. 



407 



lor A 

P=3r,i=zSv, 4= 

3X1 
*.* P = — T— ^ = 1.732 K /, whioh shows statement in brackets to be trve. 
V3 

J- ^ 
'"My. 1.738 

I, = 1.73S i In delta system. 

I^R loss in Y conneeted annatnre = 3 /y*JL 

/*i? low in A oonneoted armatnre = 3 ( -^ ) r = /,V. 




E 



A. 



J<' 


E 

1 1 ■• 


t1 ^ 








E 





E-E, 



E-E. 



FlO. 6. 



Fig. 7. 




^=V§^,= 1.732^,. 
/ JUMPBin - i.7S> X ror 9 



/ Aiimu^f 



/ AiiP0tES-l.7t>x«ory 



/Aipraa-i. Tttx y or • 




/ AMKREt-tr 



/ ampehes-* 




l>elta Connection. Star or Y Connection. 

Rhm. Sand 9. Yalnes of current in three-phase connections, where xzzyzr^z. 



%m iSkm Amata 

A. Ruckgaber 



•f AUeimatora. 



In the armature of any altemating-cnrrent dynamo or motor of either 

■ingle or polyphase the copper loss is always equiyalent to —^ , in which 

/= tots! amperes and R = the measure of resistance between leads of a 
pluse, osually taken as an ayerage of the measurements of the armature 
resifttanee of each phase. 

Let H = Resistance as measured (ayerage). 
r == Resistance per phase. 
/ = Total amperes = watts -7* yolts. 
/, =r Amperes per lead. 
t ^ Amperes per phase, in winding. 



Wkmi^m^ 



Here /= A = i ; and R-rzr 
l^R loss = /»-». 



408 



ALTERNATING-CURRENT MACHINES. 



Tw 



(Fig. 10). 
E is meMured from 1 to 3 and 2 to 4. 



T — ^ — ^'^^^^ 
JB "" Tolta 



i.=i. 



Then I*R loss = 2i7«J2 



7»J? 



31 
Fio. 10. 



Two-Ph 



friMdlnffs CoMBect«4 1m Sert 






The/i«-B loB8 = -4i*r = 



4/«r 
8 



TV 
2 



J2 1b measored from 1 to 8 and 2 to 4, 
the arerage of these two being taken 
for the yalue of R* 



Then 



J»=&±4^>=r. 



The I^R lose = -5-* 



Tlftre«-Pba«e f^tmr GosttectloB (Fig. 12). 








Then the I^^R loea = 3 iV = S /i«r = iV. 

ii i8 measured from 1 to 2^ 2 to 3, and.S to 
1, the ayerage of the three being the value 
nsed for R. 

Then B as measured =: 2 r. 

™^ ,.„, PR 

.-. The I^^R loss = -y 



Fig. 12. 
Three-Pliaae n«l«a CoMMCctfon (Fig. 18). 



Then Ii*R loss = 3 iV = 



/V 
3 



i{ is measured from 1 to 2, 2 to 3, 
and 3 to 1, the arerase of these being 
taken as the ralue of R, 




-VVWWWWW>AAA/V\r 

r 
Fio. 13. 



2^ 



r (r -\-r) 2 I^R 

Then R as measured = - ^^^i^. = - rand the Ii*B loss = -j— 



1 



REGULATORS FOR GENERATORS. 409 



Tli« General Electric GomiNUiy in October, 1889, placed on tbe market a 
lev type of polyphase alternator, which Is claimed to overcome many of 
HidfauItB common to the old Btyie of machine, eepecially when oBed on 
eomUned lighting and motor loads. While it has been found a compara- 
tive] j easy matter to compound and oTer^sompound for non-inductlTe loads. 
It has been heretofore quite difficult to add .excitation enough to oomppuna 
for indnctiTe loads which require considerably more field current than do 
leads of a non-inductive nature. 

The following description is taken from the bulletin issued by the makers 
[ deKiiblng the machine, which is of the revolving field type : — 

I "The means by which this result is accomplished are as follows : The 

i daft of the kltemator which carries the revolving field carries also the 

i aniutare of the exciter, which has the same number of poles as the alter- 

! sator, go that the two operate in synchronous relation. In addition to the 

I eommntator. which delivers current to the fields of both the exciter and the 

I altcnuUor, the exciter has three collector rings throush which It receives 

eorreotfrom one or several series transformers inserted in the lines leading 

: from the alternator. This alternating current, passing through the exciter 

'■ ■nnatore, reacts magnetically upon the exciter field in proportion to the 

rtco^ and phase relation of tne alternating current. Consequently the 

Bagaetie field and hence the voltage of the exciter, are due to the combined 

«iwt of the shunt field current ana the magnetic reaction of the alternating 

evieiit This alternating current passes through the exciter armature in 

nek t manner as to give the necessary rise of exciter voltage as the non- 

bidietfTe load increases, and without other adjustment, to give a greater 

lin of exciter voltage with additions of inductive load." 

MBQVMiA^T^mm worn AiiorsRiTATiirc} cujimKirr 



General Electric €k>mpany. 

Tbk regulator antomatically maintains the voltage of the generator at 
ws deeired value by varying tne exciter voltage. Tnls is done by rai ' " 



<9«mnf and closing a shunt circuit across the exciter field rheostat. Fig. 14 
>(ovi the elementary connections of the regulator. The rheostat shunt 
fttvit is opened and closed by a differentially wound relav. The current 
for operating this relay is taken from the exciter bos bars anu is controlled by 
ueflotting main contacts. The current for oneratins the direct-current con- 
tni msgnet is also taken from the exciter bus bars. The relay and the dlrect- 
wnnteontrol magnet constitute the direct-current oortion of the regulator, 
lid maintain not a constant but a steady exciter voltage. The alternating- 
cvrent portion of the regulator consists of a magnet having a potential 
^Bdiag connected, by means of a potential transformer, to the bus bars or 
tie elrenit to be rMuiated. This magnet also has an adjustable compen- 
Htlng winding which is connected in series with the secondary of a current 
^BMormer usually Inserted in the principal lighting circuit. The core of 
tmi magnet is attached to a pivoted lever carrying a counterweight which is 
^VBneed by the attraction of the magnet. If a load is thrown on the genera- 
tothe voltage will tend to drop, the alternating-current magnet will weaken 
^destroy Oae balance of the core and lever and cause the main contacts to 
eloie; this in turn will close the relay contacts and entirely short-circuit 
MM aciter field rheostat, thus increasing the exciter voltage until the origi- 
ui haUnce of the alternating-current magnet core and lever is restored 
^ the altematixig-earrent vmtage maintained at the required value. 

Is BOfme eases the exciter voltage will vary from 70 to 126 volts from no 
KM to full load. This is especially true if the load is partly inductive 
ttd ^e rsffulator is adjusted to compensate for the line loss. In order to 
l[tthe fall range of regulation within the scope of the regulator in such 
*SM, the alternating field rheostat should be turned entirely out and the 
*^ter field rheostat adjusted to lower the alternating-current voltage 
wont flSper cent below normal. When the regulator is switched in, it will 
CUM tbe rheostat shunt circnit and instantly build the voltage up to nor- 
^« and maintain normal voltage by rapidly opening and closing the 
rheoftat shunt circuit. --• * f ^ ^ • 




( 



410 



ALTERNATINQ-CURRENT MACHINES. 



MAIN eOtfTACTt 



0.C.0ONTM0LI 
MAONtT-*. 




m 



POTINTIAL 
MNIOSTAT 



Tcn ^ 



^=<ouiiMNT mAiiaFOf 



rvCOBHS 



ntur 



A.e. MNUMTOII 



<M MAIM 



m 



HOTOM 



Fio. 14. Diagram of Xlrrell regulator and connections for a single genera* 
tor and exciter. 

AlteimatincwCarrent Amtati 



Almost any continnons eorrent armature iHndlng may in m general way 
be naed for alternating currents, but theT are not veil suited for suoli work, 
and speoiiJ windings better adapted for the purpoee are deeianed. 

Alternating current armature windings are open^circuit wmdlngs, exeeot- 
ing in the rotary converter, where the rings are tapped directly on to tne 
direct current armature windings. 

Early forms of armature windings of this type, as first used in the United 
States, had pancake or flat coils bound on the periphery of the core, in 
the next type the coils were made In a bunched form, and secured in lane 
slots across the face of the core. Both these types were used for alngfe* 
phase machines. After the introduction of the multiphase dynamo, 



ture windings begun to be distributed in subdiyided oolis laid m slots of the 
core ; and this is the preferred method of to-day, especially so in the 



revolring field mtMshines. 

The sinffle coil per pole type of winding gires the laiver E.M.F., as the 
coils are thus best distributed for influence by the magnetic field. This type 
also produces the hishest self-induction with its attendant disadvan t Mes. 

The pan-cake and aistrihuted^oU windings are much fk^er from Belf-aidn»> 
tlon, but do not generate as high E.M.F. as does the single-ootl windings. 

In well-considered multiphase windings the E.M.F. Is but little leas for 
distributed coils than for single coils, and has other adyantagee, espedaUy 
where the use of step-up transformers permits the use of low voltages, and 
conseauently light InBulatlon for the coils. The dlstributed-ooil winding 
offers better chance for getting rid of heat from the armature core, and the 
conductor can in such case oe made of less eross'^ection than would be 
required for the single-coil windings. 
— nii^ greater numl^r of coils into which a winding is divided, the less will 



ARMATURE WINDINGS. 



411 



be tbe terminal TolUge at no load, Pantaall A Hobart gire tli« following 
fatio for termiiial roltage under no-load conditions : 

ttnsle-eoil winding =r 1. for the same total number of conduoton, the 
•pacing of eondneton being nnlform oyer the whole oircomf erenoe. 
Two-eoil winding = .707. 
Three-coil winding = .687. 
Foiii>-coil winding r= .664. 

When tbe armature ie loaded, the cturent in itreectB to change the termi- 
nal S.M.F., and this mfty be maintained constant by manipuMtion of the 
exciting current. With a glTen number of armature conductors this reac- 
tion is greatest with the single ooll per pole winding, and the ratios just 
giTen are not correct for full-load conditions. 

Mmcle-pksuMi IFImdla^.— The following diagram shows one of the 
iplest forms of single-phase winding, and is a iingle coil per pole winding. 




Fio. 10. 

Another similar winding, but with bars In place of colls, is shown in the 
nUowtng figure. It can oe used for machines of large output. 




{ 



Fto. ]& 



412 ALTERNATING-CURRENT MACHINES. 

Ttia followlnf flgnra ihawi k good (jpe of thrMban p«rpola«: 




» 



* •rinding tar 4 



llowliur dlunm il 
. It oIutiM tbe 1 



l«>d HlTaoUige, and UappllMbl* (o Miy nombat ol 



)dtj^ 



Flg^ 1tl« a dlaffam of a bar irladlng fOr 
bur oondooton p«r pole par phaae. 



'lBdlBc>. — Fig. a« li a dbwrun of a tbrM^M* 



ARHATUBE WINDINOB. 

I vliidliis eoaaacttd In T, lo wbloh ooe aad of «Beli ctf the three vtndlnn 

Eli soDBeetfld to > common taimliul, the other endi ly' '-■ — 

I tkree eoUeclor rlngi. 



■J HiIt H nf %tiM tn t*1 iMn Jth, 



the proDer eudi to sUDUect to tha common terminal and 



telbartain mm* be neleeteif u follova: Auume that the cocducCoi 

■UdLeolthepole-plecelsurTTlnffthemmxlmur 

Hub bj ui arrow ; then the current In the condu 
jMiii lo it Till be In the ume dliacUi 



amimffrinm the common termlnel, the end toward which the arrow point* 
■«tba«nm«tad to ona of therlngi, vhUa the other end is connected to 
ikaMmmon termlDftL It [• anlte u evident that the carrenta in the two 
Hijaeant coDdnoton mnit be trwjnff <nfo the common terminal, and Ihcre- 
ibte tbe nula toward vhleh the arrowi point muat tte connected to tha com- 
■OB tariDiiuJ, while their other enda are connected to the remaining two 

In a delt* winding, atarthie with tha condacton of one phase In the mid- 

Koaaafla^la conductor; then but one-half the aune lalue of current 



I 

( 



It In the other two phuw. a 



414 



ALTERNATING-CURRENT MACHINES. 




and Talae will best be shown in the following dlagrem, In whieh x nuKj 
taken as the middle eollector-rtng, and the maximam current to be flo 

from X toward z. It will be seen that no e 
is coming in over the liney. bat part of the cnrreBfc 
at » will nay e been indncea in branches b and e. 

Most three-phase windings can be oonneetod 
either in Y or delta ; but it must be borne in ntind 
that with the same windings the deltapOonnecUon 
will stand 1.732 times as much current as the T- 

connection, but gives only t-=~ as much voltagew 




FI0.2S. Path and Value 
of Current in Delta- 
eonnected Armature. 



«t«re R«SMtl*B «f 



AHe 



Since the armature core is a part of the magnetic 
circuit, and since the armature winding surrounds 
thU core and also carries current, It must b« ' 
expected that this current influences the total magnetism of the macbine J 
and hence ita yoltage. This eifect. combined with the natural IndactaDce 1 
of the winding, itself constitutes wnat is called armature reaction. Fig. 29 




■^ 



FlO. 23. 



shows an alternator in its elements. The armature winding is tapped in 
two places and connected to the collector rings d and e, from wmeh the 
current flows to the external circuit. This current passing through the 
winding on the armature creates a magneto-motlTc force, which tends to 
produce the flow of magnetism as shown by the dotted lines a — b—e; 
a' — f—e'.OT in a general direction, m—n. 

The field current proper entering at A and coming out at B tends to pro- 
duct magnetism in the direction a; —y, at right angles to m~n. Under 
such conditions, therefore, the ampere-cums of the armature are acting at 
right angles to the ampere-turns of the field. This is the condition under 
non-inductiye load, the maximam current of the armature occurring in 
time and space simaltaneoosly with the maximum E.M.F. 

If the maximam of the current of the armature occurs later than the 
maximam of the E.M.F., or in other words, if the current lags behind the 
E.M.F., the ampere-turns of the armature are no longer acting in a direo- 
tion m^n when the current is a maximum, but in a direction m' — n', 
partially opposing the main fluxx — y. If the lag of current becomes 90* 
the armature reaction would turn still more around, becoming, in fact. Just 
opposite tox — y. 

Thus, on non-inductive load, the armature ampere-turns combine with the 
field ampere-turns at right angles, and with increasing lag show a liigher 
and higher resultant until at 90^ las the two combine by direct addlUon. 
Just similar to all this is the self-induction component of the armature 
inductance. As has been pointed out, self-induction lags in its oppoeiog 



1 



ARHATURE REACTION. 



415 



■eta behind tlie oarrent, thus on non-lndootlye load, the oppoainff effect 
Elir-lndQction is shown by Fig. 24. 




Fio. 24. 

Ml a— c = /= theenrrent, 

' a— d=: J? = the E.H.F. generated by the revolutioiu of the arma- 

ture, 
a— 6 £= the reelstanoe drop = IR in phase always with the current, 
a— 17 = IX =: the inductive drop 90^ away from the oorrent. 

': The resultant of these =r a — e =: ^o = ^^^ total E.M.F. neoMsary to pro> 
bse to give the value E under the conditions. 
V Am current lags these values are as shown in Fig. 25, the current lag- 





FlO. 25. 

Ihg behind and E.M.F. bv the angle 9, At VP lag the E.M.F. of self- 
woetion is just in line with E^ hence is added directly to give the total 
EJfJ. E^ necessary to generate to product B, 

Ikos a similarity exists between the armature reactive effect shown in 
1^28 and the armature self -inductive effect shown in Figs. 24 and 25. On 
ft« aoeoimt it has been suggested by Mr. C. P. Steinmetz that the two 
Vihiai be combined into one and the combined value be given the term 
"^ndironous impedance.*' This value is obtained in an actual alternator 
^ ibort^iireniting the armature upon itself and reading the anipere-tums 
k the Held coils necessary to give full armature current, whion is then 
^i^nnedin terms of ampere-tnrns. Since on short-circuit the armature 
^•rs^oms are exactly opposing the field ampere-turns, this reading 
V^ a direct measure of the armature opposing forces, but conveniently 
^oafvted into ampere-turns. To calculate from this value the amount of 
^^oe-tums necessary in a given alternator to give a certain voltage, pro- 
*tN as follows : 

Ut A equal the ampere-turns necessary to produce the terminal voltage 
' of the alternator when running on open circuit : let B equal the syn- 
chnmoQs impedance ampere-turns obtained as above. Then the total 
— >p ere-tunis required to produce the voltage B on non-inductive load 

^'^ J^-\-B^ If the current Is not non-inductive the two values must be 
^onMned with pn^Mr phase relation, as shown in Figs. 24 and 26. The 



( 



416 



ALTERNATING-CURRENT MACHINES. 



method has been exteiulTely wed and for ordinary deeigne seems » 
nsef al one to follow. A designer can calonlate this yalne to a yecy 
aoproximatlon, thus predetermining the regulation. It can be seen __ 
tnlB that a single-phase alternator ^res a pulsating armature reactioai* 
polyphase armature ffives a constant armature reaction since it can bes 
that at any instant the magnetic resultant of the current is the same. 

For this reason, among others, a polyphase alternator is more elBcis^ 
than a single-phase macnine since the pulsating armature reaction sets i| 
eddy currents from its rarlable nature, which increases the losses. 




SYlfCHIiOintZBlift. 

There are numerous methods of determining when alternators are in sti^ 
some acoustic, but mostly using incandescent lamps as an Indioatar. -j 

In the United States it is most common to so connect up the synchroaiM 
that the lamp stavs dark at synchronism ; in England it is more usual jj 
have the lamp at full brilliancy at synchromism, and on some aoeounts la 
latter is, in the writer's opinion, the better of the two, as, if darkness ia4| 
cates synchronism, the lamp breaking its filament might cause the mnrMsn 
to be thrown together when clear out of step ; on the other hand. It is soMW 
times difficult to determine the full brilliancy. I 

The two following cuts show theory and praetice in oonneetins synehie 
nizers. 



/^ 



/^ 






i 



a 



1 



a 
b 



ft 



Fio. 26. Synchronizer Connections. 

W hen connected as ahown^ the lamp 
will thowJSUl c,p. at tynchronism. 

If a and b are reversed^ darkness of 
lamp will show synchronism. 




Fio. 27. Synchronizer Gonneetionf* 

Lamp lights to full c.p. when dgnth 
mos are in spnchronism* 



Two transformers having their primaries connected, one to the loaded 
and the other to the idle dynamo, have their secondaries connected in series 
through a lamp ; if in straight series the lamp is dark at svnohronism ; tt 
the secondaries are cross-connected the lamp lights in full brilliance sft 
synchronism. 

me I^lncolB ft jncliroBlser is so made as to move a hand around a 
dial so that the angle between the hand and the vertical is always the 
phase angle between the two sources of electro-motive force to which the 
synchronizer is connected. If the incoming alternator is runnins too fssi 
tne hand deflects in one direction, and if too slow, in the opposite airectioo. 
Coincidence in phase occurs when the moving hand stands vertically. A 
complete revolution of the hand indicates a gain or loss of one cycle in tlis 
frequency of the incoming alternator as compared with bus-bars. 



SYNCHRONIZING GENERATORS. 



417 



Bvppose a ■tationaiy coil F, Fig. 28, has suspended within it ft eoil A, free 
|o moTe ftbont an axis in the planes of both coils and including a diameter 
^ eatik. If an alternating current be passed through both coils, A will 
tike np a poeition with ito plane parallel to F. If now the currents in A 
lad F be reTersed with respect to each other, coll A will take up a position 
180^ from its former poeition. RcTenal of the relative directions of currents 
ii A and F is equivalent to changing their phase relations by 180", and 
tterefore this change of U09 in phase relations is followed by a correspond- 
fag change of 180^ in their mechanical relations. Suppose now, that instead 
of reversing the relative direction of currents in A and F^ the -change in 
pbase relanons between them be made gradually and without disturbing 
Ihe enrrent strength in either coil. It is evident that when the phase 
41iference between A and F reaches 90P the force between A and F will 
Weome reduced to zero, and a movable system, of which A may be made a 
Mrt, is in condition to take up any position demanded by any other force. 
Ml a second member of this movable system consist of coil B^ which may 
> te fastened ri^^dly to coil A, with its plane 90P from that of coil A, and the 
mk of A passing through a diameter of B. 
liuther, suppose a current to circulate 
Afough Bf whose dlif erence in phase rela- 
tire to that in A^ is always 90°. It is evident 
•Oder these conditions that when thediffer- 
eoee in phase between A and F is 90Pf the 
BOTsble system will take up a position 
laeh that B is parallel to F, because the 
force between A and F is zero, and the force 
betveen B and i^ is a maximum ; similarly 
vbien the difference in phase between B 
and j* is 90°, A will be parallel to F. That 
ii, beginnine with a pnase difference be- 
tween A ajxaF of 0, a phase change of 90" 
vill be followed by a mechanical change 
OB the movable system of 90°, and each suc- 
eeiriTe change of 90° in phase will be 

followed by a corresponding mechanical FiO.28. Lincoln Synchroniser, 
change of 90°. For Intermediate phase 

relations it can be proved that under certain conditions the position of 
equilibrium assamecf by the movable element will exactly represent the 
JMttte relations. That is, with proper design, the mechanical angle between 
the plane of F and that of A and also between the plane of F and that of B 
is alvays equal to the phase angle between the current flowing in F and 
thoee in A and B respectively. „ , . ^ . . 

As commercially constructed coil F consists of a small laminated iron 
fleld-maniet with a winding whose terminals are connected with binding 
posts. The coils A and B are windings practicallv 90° apart on a laminated 
iron armature pivoted between the poles of the magnet. These two 
windings are Joined, and a tap from the Junction is brought out through a 
•lip-ring to one of two other binding posts. The two remaining ends are 
biwttht out through two more slip-rings, one of which is connected to the 
nnuuning binding post, through a non-inductive resistance, and the other 
to the same binding post through an inductive resistance. A light 
almniniim hand attached to the armature shaft marks the position assumed 
bj y^ armature. 





nrovcTom typb sinsrcHiftOftcoPiB. 

From T%« KUetric JoumcU. 

This type is especially applicable where voltage transformers are already 
fantalled for use with other meters. As It requires only about ten apparent 
watts It may be used on the same transformers with other meters. There 
are three stationary colls, N, M and C, Fig. 29, and a moving system com^ 
prtsing an iron armature, A, rigidly attached to a shaft, 5r, suitably pi^pt^ 
and mounted in bearings. A pointer, B^ is also attached to the shaft S, 
The moving system is balanced and is not subjected to any restraining 



418 



ALTERNATING-CURRENT MACHINES. 



forc«, iQoh as a •pring or gravity oontrol. The axes of the eoil« J^aad 
are iu the same Tertloal plane, bat 90 degreee apart, while the axle of Cla 
a horisontal plane. The ooils JVand M are connected in " split phase ** r ~ 
tion through an indnctire resistance P and non-indnotire resistance Q^ 
these two circuits are paralleled across the bus-bar terminals 8 and 4 of 
synchroscope. Coil C is connected through a non-inductive reirist 
across the upper or machine terminals 1 and 2 of the synchroscope. 

In operation, current in the coil C magnetises the iron core carried 
the shaft and the two projections, marked A and ** Iron Armature** In 
S9. There is, however, no tendency to rotate the shaft. If current 

Sassed through one of the other colls, say if, a magnetic field will be 
uoed parallel with its axis. This will act on the projections of the 
armature, causing it to turn so that the positive and negative pro|eei 
assume their appropriate position in the field of the coil M, A reversal 



lO— I OS 



Pdnlar-Brt 




^baft-B 



Iron Amutiara 




FfO. 29. 



the direction of the current in both colls will obviously not aifect the posi- 
tion of the armature : hence alternating current of the same frequency and ' 
phase in the coils C and M cause the same directional effect upon the^ 
armature as if direct current were passed through the coils. If current ^ 
la^ng 90 dsfrees behind that in the coils ^and C be passed through tiie^ 
eoU N^ it wfll cause no rotative effect upon the armature because the 
maximum value of the field which it produces will occur at the instant 
when the pole strength of the armature Is sero. The two currents in the 
coils M and N produce a shifting magnetic field which rotates about the* 
shaft as an axis. As all currents are assumed to be of the same frequency, 
the rate of rotation of this field is such that its direction oorresponds witti 
that of the armature projections at the instants when the poles induced in 
them by the current in the coll C are at maximum value and the field ahlfts 
through 180 degrees in the same interval as is required for reversal of the 
poles. This is the essential feature of the instrument, namely, that the 
armature projections take a position in the rotating magnetic field which ' 
corresponoa to the direction of the field at the instant when the prolectlons 
are magnetised to their maximum strength by current in the coil C If 
the freqnwioy of the currents in the coils which produce the shifting field Is 
less than that in the coil which magnetises the armature, then the arma- 
ture must turn In order that it may be parallel with the field when its poles 



^ 



PARALLEL OPERATION. 419 

I 

Joe lU muTlimifn strengtii, cooMqnently rotation of its annature indicates 
Fa differenee in frequency, and the direction and rate of rotation show, 
[THpectirely, which current has the higher frequency and the amount of 
the difference. 



Maim om tk« Par»ll«l KaBatafl* of Alt«nufctom. — There is 

Uttie if any tronhle in running alternators that are drlren hy water-wheels, 
oving to the uniform motion of rotation. With steam-engine driren ma- 
^iaes it is somewhat different, owin^ to more or less pulsation during a 
itroke of the engines, caused hy periodic variations in the cnfc-oiT, wmeb 
eaose oscillations in the relatiTe motion of the two or more machines, 
•eeompanied by periodic cross currents. Experiments haye prored that a 
fllsggisli governor for engines driving alternators in juir^el is more desi* 
tibfe than one that acts too quickly ; and it is sometimes an advantage to 
9pftf a dashpot to a quick-acting governor, one that will allow of adjust* 
BeDt while running, it is quite desirable also that the governors of engines 
designed to drive alternators in parallel shall be so planned as to allow of 
sdjiistment of speed while the engine is running, so that engines as well as 
djiuunos may be synchronized, and load may be transferred from one 
nachine to the others in shutting down. Foreign builders apply a bell con- 
tact to the same part of all engines that are to be used in this way, and throw 
■seUnes together when the bells ring at the same time. These bells would 
abo wrre to determine any variation, if not too small, in the speed of the 
Mfiiines, and assist in close adjustment. 

Haanfacturers do not entirely agree as to the exact allowance permissible 
for Tviation in angular speed of engines, some preferring to design their 
djinanos for larse synchronizinc power, and relatively wide variation in 
ttgnUr speed, while othen call ror very 'Close reg^ation in angular varia- 
mi of Mgine speed, and construct their dynamos with relatively little syn- 
duonlang power. 

I>7namos of low armature reaction have large synohronising power, but if 
uodentslly thrown out of step are liable to neavy cross-currents. On the 
Motnrr, machines with high armature reaction have relatively little syn- 
cfatoDlAng power, and are less liable to trouble if accidentally thrown out 
ofEtep. 

The uutller the number of poles the greater may be the angular variation 
wtTeen two machines without causing trouble, thus low frequencies are 
more favorable to parallel oi>eration than high ; and this is especially so 
where the dynamos are used to deliver current to synchronous motors or 
rotary converters. 

8peeifleations for engines should read in such a manner as to require not 
Bore than a certain stated angular variation of speed during any stroke of 
the machine, and this variation is usually stated in degrees departure from 
Aneanipeed. 

Tlie General Electric Company states it as follows : — 

"We have . . . fixed upon two and one-half degrees of phase departure 
trom a mean as the limit allowable in ordinary cases. It will, in certain 
^*Mi, be possible to operate satisfactorily in parallel, or to run synchronous 
apparatus from machines whose angular variation exceeds this amount, 
ud in other cases it will be easy and desirable to obtain a better speed con- 
[nd. The two and one-half degree limit is intended to imply that the max- 
u&om departure from the mean position during any revolution shall not 

cxMed ^ of an angle corresponding to two poles of a machine. The angle 

of dreiunf erence which corresponds to the two and one-half degrees of 
me variation can be ascertained by dividing two and one-half bv one-half 
the number of poles : thus, in a twenty-pole machine, the allowable angular 

variation from the mean would be r^ = .25 of one degree." 

Some foreign builders of engines state the conditions as follows : Galling N 
thenmnber of revolutions per minute, the weight of all the rotary parts of 
the engine should be such that under normal loiul the variation in speed dur- 
ing one revolution ^"^'""^ *"***' will not exceed ~ - Some state ^ - 

N average 250 200 

Oadin says : " The rc«ulatlon of an engine can be expressed as a percent- 
Sfo of variation frcnn that of an absolutely uniform rotative speed . A close 
Bolitionof the general problem shows that 1\° of phase displacement cor- 



( 



420 



ALTERNATING-CURRENT MACHINES. 



responds to a speed yariation, or *' pulsation/* with an alternator of two ■ 
poles, as follows : — 

2 75^ 
In the case of a single cylinder or tandem compound engine * 



A cross compound 



ft 
5.5% 



A working out of the problem also shows . . . that no better reaolts are 
obtained from a three-crank engine than a two-crank. 

The Westinffhouse Company designs its machines with larger syDehro- 
nizing effect oy special construction between poles, and allows aomewhat 
larger angular yariation, stating it as follows: The variation of the Ay* 
■ wheel through the revolution at any load not exceeding 25% overload, shaU 
not exceed on&-sixtleth of the pll^h angle between two oouBecutive pc*l« 
from the position it would have if the motion were absolutely uniform at 
the same mean velocity. The maximum allowable variation, which i» the 
amount which the armature forges ahead plus the amount which It h»M 
behind the position of absolute uniform motion is therefore one-thirUeth of 
the pitch angle between two poles. 

The number of degrees of the circumference equal to one-thirtieth of the 
pitch angle is the quotient of 12 divided by the number of poles. 

The cross currents of alternators can be shown by reference to Fig. 39t 




Fio. 30. 



6 6 



which represents the E.M.F. vectors of two alternators which have swung 
apart in phase due to any cause, such as variation in speed of their prims 

movers or fluctuations of speed during a revoln- 
I tion. 

a I b Let O^A = E.M.F. vector of alternator A. 

O—B =. E.M.F. vector of alternator S, 

As drawn, the vectors are displaced in phase by 
the angle 0. When theee alternators are con- 
nected In multiple there will be acting between 
them the E.M.F. ^ — 2?, or drawn to the center 
point O, the E.M.F. O ^ D. This E.M.F. acts 
through the two armatures in series, the oireuit 
being a — h — c — d, (Fig. 31); the current result- 
ing is equal to the volts O — D divided by the im- 
pedance of the two armatures in series, which is 
equal to 

V(/2. + /?»)« + (2 ir/Za + 2 ir/i*)a 

where JU and Jtb = the resistance of the two al- 
ternator armatures respectively and Im and I* 
their inductances. 

Since in such a circuit the proportion of inductance is greater than the 
resistance, the current flowing from the E.M.F. O — Z> is lagging a large 
amount as shown by the line O— C. Hence the £ Jd.F.'s O — ^ and O — J 



Fig. 31. Two Alterna- 
tors Connected in 
Multiple. 



ALTERNATING-CURRENT MOTORS. 421 

of the alternators proper are In phaae approximately with this cro«B carreat 
and henoe onder sach conditions as the figure indicates there will be an ex- 
dian^ of energy (since E.M.F. and current are in phase) which is what 
actually happens, thus tending to bring the two aitemators together in 
phase. 
Fig. 32 shows the vectors of two alternators A and B in phase but the 



».B 



FlO. 32. 

IJf.F. — A smaller than the other, O — B, due, for instance, to the field 
(A one being weaker than that of the other. In this case there is a difference 
of O—D volts to act through the armatures of the two aitemators in 
■erics, as in Fig. 31. As shown in Fig. 32 the current from this E.M.F. 
O—D bigs 9fP and is indicated by the vector O— C. This current is, how- 
«Tflr,90° away from the £.M.F.*s O^ A and O — B of the machine proper 
and httioe does not represent an exchange of energy ; therefore, it nas no 
tendency to bring the machines together or increasing the dephasing. 



It is plain from the foregoing that to connect an idle alternator in 
panllel with one or more already in use : 

£zdte the fields of the idle machine until at full speed the Indicator 
ikovs bns-bar pressure, or the pressure that may have been determined 
on as the best lor connecting the particular design of alternator in circuit. 

Connect in the synchronizer to show when the machines are in step, at 
which point the idle machine may be conneoted to the bus bars. The load 
viB now be unequally divided, and must be equalized by increasing the driv- 
liVhpower of the idle dynamo until it talces on its proper part of the load. 

vsrv little control over the load can be had from the field rheostats. 

To aiseonnect an alternator from the bus-bars : Decrease its driving power 
ilovly until the other machines have taken all the load from it, when its 
lain switch may be opened and the dynamo stopped and laid off. 

Ibe single-phaee alternating-current motor has been quite well developed 
vuing the last few years, but it has as yet come Into rather limited use. 
rbe polyphase motor has come into very general use, its relative simplicity 
Aelng a strong feature. 

Only the most elementary formulsa will be given here, and the reader is 
nferred to the numerous books treating on the subject ; among others, 
8. P. Thompson, Steinmetz, Jackson, Kapp and Oudin. 

Following is a statement of the theory of the polyphase motor, condensed 
from a pamphlet of the Westinghouse Electric and Manufacturing Com- 
Ptty. 




< 



I 



ALTERNATING-CURRENT MACHINES. 



nMry "Tliecr; of the P*lj|ik«aa Xa<l«(;tl*M 91***r. 

ins4ho« magnet bo held 01 



be mada to flow about eltherone or the saU ot pole* HparatalT. Che di 
will Uke lu poaitlon pumllsl iritta the line* of forua that mar ba flowlB 
will be Hen Dj tba following agurea. 



U the two Hts of pole* are eiolted at the >ama tima by curreDti of sqnal 
■tnngth, tben the needla will take Ita iHHitlao diagonaJlr. half wa; ba- 
tween the two aeU of polee, u will be aean by tiie [ol lowing diagnm. 

It la now eaiilT coDcelrable that If one of theaa anrrants la gnwiiit 
■ttoiuer while thaotheiiaattbeutmeUme 
beeomlng weaker, the oeedle will ba at- 
trsotad toward the former nnttl it reaohaa 
it* mailianm Talne, wheo if tba currants 

reached^iU laailmum btsioa to weaken, 
and the other cnrreDt having Dol only re- 
vaned Ite direction but begun to grow 
Itrong. attnota the needle away troTn (be 
Brat catrent and In tha aame direction o< 
roMIlon. If thig proceea ba aontlnuallr 
r«>eated, tba Beedla will eootlnaa to re- 
•Dire, and Itt direotiOD of rotation will be 
determined b; the ' 



h»e windlnn, which wt 11 react on tba Said windings, and roUUonwUl 
« produced In the core ]uit m It waa !n the eompaM needle. Two cranlu 
it right anglea en an engine abaft ara »nnlogoua with tha qnutor-phaia 



Vh^owy of the Polyphftafl lAAacitloB M«t«r. 

Condensed from C. P. »telnmeti. 

id eymbola are uaed for deelgnatlng the parta tod 



THE INDUCTION MOTOR. 423 



R= stattonaiy part, nearly always oorrespondlng to the field. 
Boior ^ lotatiBg part, oorraipoadlng to tlie armature of the dlreot-emrent 



Ajaaljtlcttl leummwj vi ]P*Iypkaa« Ijadvctloii Motor. 

Let r = resistance per olreult ofpHmory, 

Ti = re^tanoe per oircuit oi seoonaary, 

being redaeed to primary system by square of the ratio of turns. 

Ijet p = number of poles, 

X = react anee w. primary t per oirenit, 
f Xi = reactance of secondary ^ per circuit. 



rsdoeed to primary system by square of the ratio of turns. 

list J =: per cent of slip, 

I = current per circ 
B =z applied E.M.F. per circuit, 



J = current per circuit of primary ^ 

'E.M.F. perc' 
Z = impedance of whole motor per circuit, 



T^ torque between the stator aud rotor t 
f ss freqaetiey of applied B.M.F. 

Lst the primary and secondary consist of m circuits on an m phase system. 

n := primary turns per circuit, 
»!=: secondary turns per circuit. 

Let a := — ratio of transformation. 

Then 

sE 

/(neglecting ex. current) = V / ■ v« i ^/ i ^^^ • 

_, -,_ mpr^E^B 

Torque r^ 4ir/ [(n + ,r)« + *"(uri + ar)»] ' 

Power - ^^i^'O-'y . 
mpE^ 

Starting current s= i =r ^ * 




Starting torque = q(^ X ^,- 



Note that the maximum torque is independent of ieoondary reaiatanee r^, m 

depends on the tecondary re$iitance» W 



sod thus the speed at maximum torque depends on the tecondary retietance* 
Current at maximum torque is also independent of secondary resistance. 



Hie maximum torque occurs at a lower speed than the maximum output. 
A resistance can be chosen that when Inserted in the secondary, the maxlmmq 



424 



ALTERNATING-CURRENT MACHINES. 



torqae will be obtained at startlxig ; that is, the speed at irhioh 
torque oooors can be regulated by the reslstanee In the xotor. 




ViQ, 36. Torque otmres for Polyphase Indnotion Motor. 

Onnres 1, 2, and 3 show the effect of suooesslTe increases of rotor reals*- 
anoe, rotor rnn on part of cnrre o-^ ; for here a decrease of speed dne to 
load increases the torque. 

Spe«id of Indaction Motor.— The speed or rotating Tolooitj of 
the magnetic field of an Induction motor depends upon the frequency 
(cycles per second) of the alternating current in the field, and the nvaalmr 
of poles in the field frame, and may be expressed as follows :— 

r.p.m. = reyolutionfl per minute of the magnetic lleld» 
p = number of poles, 
/= frequency; then 

r.p.m. = 120 "^ 
P 

The actual revolutions of the rotor will be less than shown by the formula, 
owing to the glip which is expressed in a pero«itage of the actual revoln- 
tions ; therefore the actual revolutions at any portion of the load on a 
motor will be 

r.p.m. X 9l^ due to the part of the load actually in use. 

actual speed = r.p.m. (1 — % of slip.) 

The following table by Wiener, in the American BUetrieicm, shows the 
speeds due to dBf erent numbers of poles at various frequencies. 



•poodi of Jtotakry 



Field for I»lireroBt ITaasbo 
for Vttrioiia JProqvoBcioa. 



ra of Poloa 



^ 


Speed of Revolving Magnetism, in Revolutions per Minute, when 


li 


Frequency is : 


Is 
j5 


25 


30 


33i 


40 


50 


60 


66} 


80 


100 


120 


125 


133J 


2 


1500 


1870 


2000 


2400 


3000 


3600 


4000 


4800 


6000 


7200 


7500 


8000 


4 


750 


900 


1000 


1200 


IGOO 


1800 


2000 


2400 


3000 


3600 


S760 


4000 


6 


500 


600 


667 


800 


1000 


1200 


1333 


1600 


2000 


2400 


2600 


2067 


8 


375 


450 


500 


600 


750 


900 


1000 


1200 


1500 


1800 


1875 


2000 


10 


300 


360 


400 


480 


600 


720 


800 


960 


1200 


1440 


1500 


1600 


12 


2S0 


300 


333 


400 


500 


flOO 


667 


800 


1000 


1200 


1260 


1383 


14 


214 


257 


286 


343 


428 


514 


571 


686 


857 


1029 


1071 


1143 


16 


188 


225 


260 


300 


375 


460 


600 


600 


750 


900 


938 


1000 


18 


167 


200 


222 


267 


333 


400 


444 


533 


667 


800 


833 


889 


20 


150 


180 


200 


240 


300 


360 


400 


480 


600 


720 


760 


309 


22 


136 


164 


182 


217 


273 


327 


364 


436 


645 


666 


682 


720 


M 


125 


160 


167 


200 


260 


300 333 


400 


600 


eoo 


626 


66r 










1 












' 



THE INDUCTION MOTOR. 



I. — Tlw Mp, or dWoraiM 

. lor, 1a da« to tha rMUtuia" 

BUp TBrI<« from 1 pw oent In 
-wWljrtorti 



« of TOteUon betWNO roMitaMi iotd 



, J Jaglpiod lor Yuy clou rsgnlatfon 

> 40 par cent tn onfl twllj doBicBfld, ordcfllnedfoTH>nieip«cl»l purpo**- 
WiiBat (tf as Om fallowing Mbls u embodfln^ Che ufoti TUJUIon* : 



O^iHdtrofHotor.HJ. 


Blip, at full iMul, p«r oant. 








CulUmllik 


AY»™^ 


i 


30 tow 


30 


I 




XI 


1 


» " ao 


IS 


l' 


* " " 


U 








s 




19 


s 


T » 16 


11 


T) 


' " " 


10 


m' 




* 


16 


'■ 11 




SO 


4 " 10 




ao 


8 ■■ 


e 


EO 




B 


TB 






im 


1 " « 




uo 


I |. E 


S 


a» 




3A 


300 


1 " 3 





ud the ■rnuLtore core, or Botor, 

The niodins) Id both ettrt an 
ud For Ihli reH»a both psr^ ■ 
Uk meptlon of tha winding 



— BoA t1i« Deld-tnms ooro. or SUUor, 
built npof Laminated Iron punchLcgi la 

■"■--•—"- i.-.—- ,o( either part. 



i 






,gt. Th«followiiigcul^tak 
■anal lorm ol aloii uimL 



FiOB. 37 and 88. Forma of Pouchlnga of Indnotlon Hoton. 



nu number of iloti Id tbe tliiAn- mnit he amaltlple ot ' 
aadnnnbet of phaM, and Welaetglveg the following tH 
<an EleetrieUD, u inowlng the proper Dombar to be ns 
1— i .._ . tiir^^piuua maehlnea. In practice tl 



( 



u> dealgned m Co be eqnall]' ipiiaed at 



li the whole Innef 



426 



AI/TERNATINQ-CURRENT MACHINES. 



9 mf n«ti to VIaM-Vi 



Capaeitj of Motor. 


Number of 
Poles. 


Blots per 
Pole. 


Bloti per Pole per Phue. 


TWD^hMO. 


Tliree-PhMe. 


i HJP. to 1 H.P. 


4to< 


8 

4 


J» 


1 


|H.P.tolH.P. 


4to< 


6 
6 


l» 


2 




4tol0 


5 

6 


? 


"i 


2 HJr. to 6 H.P. 


4to6 


7 
8 

9 




3 


6H.P.tofiOH.P. 


• to 13 


7 
8 
9 


4 


"i 


4to8 


10 
11 
13 




1 




10 to 90 


7 
8 
9 




3 


60HJ».to200H.P. 


8tol3 


10 
11 
12 
18 


6 

6| 


4 




<tolO 


14 

15 
16 


7 


7 



The number of nlots per pole per phase in the rotor must be prime to thft[ 
of the MkUor in order to arold dead points in startingf and to insnre smooUi 
running, and commonlv ranse from 7 to times the number of poles, or 
any integer not divisible by the number of poles, in the squirrel cags or 
single conductor per slot windings. The proper number ox slots may M 
taken from the followiug table by Wiener : 



^ 



THB INDUCTION MOTOR. 



427 



ib«r mi 



op to A H.P. Gapacliy. 



Number 

of 
PoIeSf p. 


Limits of Slota, 

Number 

7 p. to 9 p. 


Number of Rotor Slots. 


4 
6 
8 


28 to 96 
42 " 54 
66 " 72 


29| SO, 31, 33, 34, 36, 37. 

43, 44, 46, 46, 47, 49, 50, 61, 62, 63. 

67,68,60,60,61,62,63,65,66,67, 68, 69, 70,71. 



In larse machines, where there is more than one conductor in each slot 
apd fai which the winding is connected In parallel, the number of slots in 
toe rotor most be a multiple of both the number of phases and the number 
MjuifB of poles. 

The following table glTes numbers of slots for yarlous field-slots : 



MmwAmr of IKotoiHiloto 



for iBdnctloi 
over A K.P. 



Motors of Cs^iMscitioa 



Kmnber of 

FMd-SIotsper 

Pole. 



8 
9 
10 
12 
14 
15 
16 



Number of Botor-Slots. (n« = number of 
Field-Slots.) 




JRu OoMfli^. — This must be settled for each particular case, as it 
nU be governed much by the quality of iron and the particular design of 
toezaotor. 

Hysteresis loss increases as the 1.6 power of the flux density ; and eddy 
cvnnt lasses are proportional to the square of the density and also to the 
M^re of the frequency. 

The following table shows practical ralues : 

for IndnctloB 

(Wiener.) 



GMMdty 

<rf 
Motor, 



Flux-Density, In Lines of Force per Square Inch. 



For Frequencies 
from 25 to 40. 



Practieal 
Values. 



ISOOOto 18000 
15000" 25000 
18000" 32000 



Arer- 
age. 



15000 
20000 

26000 



For Frequencies 
from 60 to 100. 



Practical 
Values. 



10000 to 15000 
1200O *• 18000 
16000 " 26000 



Aver- 
age. 



12500 
15000 
200OO 



For Frequencies 
from 120 to 180. 



Practical 
Values. 



7000 to llOOO 
7500 •* 12500 
8O0O '* 17000 



Aver- 
Age. 



9000 
10000 
12500 





( 



ALTEBNATING-CDRRENT MACHINES 



■1 


■■•VnoittM for 




Moten-(a>ii«awd 


>)■ 




Flnl-DWMlty. In Una <rf Force per Squre Inch. 


C«pMity 


For FreqneDole* 




trom^Uiim. 




fromlGtoW. 


IramOOtolOO. 


HJP^' 












FTMtiail 


Ater. 


Prutloal 


Atw- 


PrmoMol 


ATar- 








V»lu«. 


nge. 


VHOM. 


age. 


J 


!000ou> Mon 


30000 


18000 to 32000 


25000 


9000 h> 31000 


uooo 






asooo 




' 40000 




10000 " »ooo 


ITBOO 




30000" BOOB 






M00( 




11000 ■' 29000 


mo* 


10 


toouo" eocoo 










12S00 " MSOO 




9D 


soooo" Toooo 


60000 








16000 II 36001 




SO 


wooo" aoooo 


70000 


MCN» 








KEOO 


100 


roooo" 90000 




iSOOO 


09000 


G6000 


2O0OO " wou 




ISO 


wooo" 100000 




50000 


TOOOO 


OOOOO 


26000 •' «00» 




aoot 


OOOOO " 110000 


100000 




TOOOO 


30000 '■ 60000 


«w» 



I 



In tba earlier ind action moloi 
to connect the drlrlnB correnC 
hlgh]]r Important that 
Iha number of wlDdlnga 
on (he ralor be prime to 
that uf Che italor. Fig. » 



otCL- 

i.belDgSl.orthrea 

Mlator winding! 

at either enj to A 
copper ring, thti 



heavy copper 

In the modem ma- 
ehinei the winding 
■hown would be In coUe 

end* being curled to 

outalde of tbe machine 
Infltead of to rlnm ■■ 

e laced on the rotor and 
9 made of ban ai men- 
tioned. 

StarMMf ud H«ir- 
slaMiMr DwTlcda. — Small 
eltj. are alartAd by closing (he c 



noton, up to about S h. p. oap*- 
:tlj to the motor. In large mn- 
if atandlng. and woald act In a 
itj of a atatlc tranaformer. and 

« method with tbe Oeoetal 



ny. A get of strongly conflrucled tealetancfa Ib ae«at 
rtnv, and lo arranged with a leTer that they niar be cla 
id after the motor baa reached iti toll apeed. These r«l 



THE INDUCTION MOTOR. 429 

i 

rncM are in Che armatoreoirtfaits. In order toglre maTJmqm ttarting torque 
ilotal armature reaiatanoe should be 

\ Whwe rj = rotor realstanoe per circuit rednoed to fieM system. 
Xx = rotor reactance per circuit redueed to field system, 
r = reaiatanoe per field circuit. 
y = reactance per field circuit. 

i Ttdi method serves the double purpose of keeping down the starting cur- 
i xtnt snd increaaing the starting torque. 



AcaUt«MC«« isi 0t«t«r. — Besistance boxes may be connected in the 
ciicults supplying induction motors: three separate resistances in three- 
fbase circuits, and two separate resistances in two-phase circuits. They 
Hwt be all eonneeted in such a manner as to be operated in unison. Under 
thsie conditions the pressure at the field terminals is reduced, as is of course 
tks starting onrrent and the starting torqae. In order to start a heavy load, 
ader this arrangement, a heavy starting-eurrent is necessary. 

CawpsiMasitaM ot A««e-Tni«af<»ms«i«.— This method is greatly 
fiTored oy the Westinghouse Electric Manufacturing Company, and is used 
extensively by the General Electric Company. It consists of connecting an 
iiKptdanee coil across the line terminals, the motor being fed, in starting, 
from some point on the windinff where the pressure is considerably less 
thaa line pressure. This avoids neavy drafts of current from the line, thus 
not disturbing other appliances attached thereto, but as regards starting 
eaxrent and torque has the same effect as resistances directly in the line ; 



that is, greatly reduces both. 
■•(•r WfaMllmn C^a 

psrt of the rotor windings are designed to be connected' in series when 



■•(•r Wfaasilmn C^nssBntsstod. — In this arrangement all or a 



■tsilhig, and are thrown in parallel after standard speed is attained. 
Another design haa part of the conductors arranged in opposition to the 
raasinder in starting, but all are thrown in parallel in regular order when 
nniiing at standara speed. These commutated arrangements have not 
hew much used in the United States. 

The lioale-phaae alternating-current motor brought out by the Wagner 
Beetiie Hannf acturing Company of St. Louis, is, in mechanical construc- 
tion, similar in many respects to the two and 
three-phase motors on the market. A field is 
built up of iron plates very much like ^ of Fig. 
40, and an armature core is also built up from 
iron plates very much like B. 

The field is wound with so-called pan-cake coils 
threading through the slots of the punching, as 
shown at C, thus producing a magnetic pole of 
intensity, varying from a maximum along the 
radius x —yio sero along the radius x — z. The 
armature core is wound with an ordinary direct- 
current progressive winding, connected up to a 
commutator in exactly the same fashion as is the 
direct-current motor winding. 
Pig, 40^ The commutator of this armature is so designed 

that it may be completely short-circuited by intro- 
ducing into it a short-circuiting circle of copper 
B^JDents. When so short-circuited, the winding affords a substitute for the 
■qmrrel-cage form of winding, above described, differing from the squirrel 
^, in that instead of currents being able to select paths for themselves, 
they are restricted to flowing in paths afforded bv the individual coils. The 
('Ps^tionof this motor, as stated, is based wholly upon the principle that 
sntadoetion motor with a completely short-circuited armature will, when 
j9 to the running speed, operate on single-phase current supply in exactly 
ue same manner as does a two or -three-phase motor with two or three- 
PhJJB current supply. 

Ths armature winding is short-circuited through carbon brushes bearing 
^KHB^e commutator surface, and the currents flowing in it are generated 
^1 uMTOCtion from the fleld. These currents flow out through the carbon 
i^vlies either into an outside resistance box, or where a direct short cir- 






ALTEHNATINO-CUBRBNT UACBINE8. 



one bnub ami back into Of 



onlt of tba bnuhM li piorlded, oat tbroturh one bnu 

anuatore thrauch tbe otber. By tha thUSng of ttw „ 

mutator ■nrlaoe, tbaj are forced Uj take audi poaitlou relatiTS Xl . 

nellc polaa cif tb« flald, that T«pallant action bMvsttn them and th« pols 

of tha field! ta oBected, and rotaUon reaolM. Who ' ' *- 

atlalnsd. tba bnuhea are no longer reqnlred and tha i 
completetv ahart-olrcnlled, u atated. The -*- — ' -'— 
up of ■Biall copper llnki, vhloh Unki, being 



ildi ta etiected, and rotaUon reaolta. When muDliig apaed la 

. tba bnuhea are no longer reqnlred and the armBtnro wlndl — '- 

iletetv ahort-olrcnlled, u atated. The ihortHilroiiltlna ring la i 

' aBiall copper llnka, vhloh llnka, being In torn mounted npnn a el 

Lltiogbaod, are thrown Into the annular opeulng in the commutator and 

br making cloae contaat with the Indlildual eeoraaDti, produce aTarrelTee- 
tlTe Bhort-olroultliig of tbe entire armature winding. In the operation of 
the motor, It la Tery adrantageona to have thla abort-clrcnltlng operalioB 
perforniadeltherat or aUghtlylwloir tbe running apeed, ao tbeee motors an 
bnllt Kith an aatomatli: deilte for performing thla operation. This deTka 
oonalate of a aet of fforemor walghte acting against a spiral spring. The 
aentrlfngal aotloD of tbe weight will, at the proper speed, force tbe iboct- 



|) 



Fio. 41. Oroae 8eatlan of Wagoer Motor. 
eirculting links Into the commutator, agalnai 



gramj^FlR. 



dinKrnmtnAtlc mnCoT be^nff aliunn aa In the starting 
diagram at the right abuwlng the conditinn at tbe aj 
attained full rimnTag speed and the cammutstor Is ahoi 



:[Ian of the Wagner motor, and the dl 

ting condlllon, and U 
- -irnialure after It hi 
irtHilrcuited. 



Alternators are convertlblH Into motors ; and one alternator win run iB , 
synchrontsni wUb another almlliir machine after it Is brought to the asma 
apeed, or. If of unlike number of poles, to some multiple of the (peed of the , 
drlleu dynamo, provided the number of pairs of poles on the motor il 



SYNCHRONOUS MOTORa. 



no. 43. Connsctlcnu ol Winner 9liigl»-Phue Mat 



Aflifbla [nto tb'e moltipla. finch motors «fll run u It se4rsd to tbe drlToo ^| 

itnuusTu up to tiro or thrsa timta ita Bannk] rull torque or capacitr. ^H 

mulfrphMa (TiiehroiMnii nioton have no atutlng-torque, but iTncbronona ^H 

BOton for nmltlpbaM clrcnlla will come ap to ijjichroDlnn irllhont mocb V 

nd, gMu Kbont left Martloa-torqne, atutlna u Induetiou motora, with ™ I 
tluj.«.aelda[isa. 

When coDDSOtod to li»a on which are connecMd iudoctlon moton that 
ttadtoeatas l^alnK cnrreiiU and low-power factor ot the line, orer eiclta- 

tloi ot the ■jncliTOnona motor fields scti In tbe lame manner aA a condenser ^ I 

(■aodiieed tn tb« Une, and toida to reatore tbe current to pb»e with the M 

ln|niH<l KM.W., and therefore to do away with IndncltTe dlstarbaiHea. ■ 

rtliaeoeaBarytoproTlde some sonrco from vblcb ma; be obtained con- H 

tUDDaiiuTeDtforeisltlnctbetleldsof tbe irnchronaDs motor; and this Is «J 

"(tsust dinio bj the nio of a small d. c. dynamo belted from the motor- ^ 
■Hft, the exeltlns onrrent not being put Into use tudl the motor annalare 
nsehis STDBlinHiEm. 

In ttartbig ■ ■jnohTownis motor tbe Held li op«n-clrcnlt«d. and current Is 

trnsd on the snnatore. lupraetlce, Seldcolls areconnectedlDTarloiuwars .1 

h oMats the duinrs otlsdnaed Toltage, and a low reslstunce coll similar M 

tBlheseriiBwliidingof thed.cnmcblneissometlmeesoarrangedonthefleld ■ 

Mm as to gl*a the necewarj reaction for gtartlng. Another waj is to ns« ■ 

alow-sTSssnre eicltfttlod. and therefore few turns on tbe Held eo!U : aleo ^ 

O* Held coOs are " split np " hj a switch at starting. The Deld eidutlon li >^ 
Unwn on after tbe rolstlni part approaches sTnchronlsm, which may be 
wUoated br a lamp or other loltable derlce at the operating switchboard. 
.CouMerablo care most b« siercised In tbenssotsTnohrouons motors, and 

uslt best eondiUoo Is where the load Is quite steady, othsrwlsa they iulro- A 

due IndnctlTe effeets on the line tbM ars qaite tronblssome. The Held of M 

•Hb a molar emx be adjusted for a wtlcular load, so there will be neither ■ 

ludlu nor lantng current, but onlty power factor. If the load change*, V 
thsnlhepawwfactoraUo changes, nntll thefleld is readjusted; If tbeload 



432 



ALTERNATING-CURRENT MACHINES. 



has b66n leseenod the curreiit will lead, and if it inoreaaes the curreot 
lag. If indaotion motors are connected to the same line, with a syncl 
nous motor that has a steady load, then the field of the synchronous mot 
can he over-excited to produce a leading current, which will conteraet 
effect of the lagging currents induced bv the induction motors. If two or n 
synchronous motors are connected to the same circuit, and the load on oi 
of them is quite variable, and its field is not changed to meet such chi 
conditions, a pumping efrect is liable to take place in the other motors, 
especial proyfolon nas been made in the design of the motors to prevent it. 
is only necessary to arrange one of the motors of the number for preventi 
this trouble, but better to make all alike. A copper shield between pol< 
pieces, and covering a portion of the pole-tip, will prevent the trouble ; 
the Westinghouse £lectric and Manufacturing Company use a heavy eoi . 
strap around each pole-piece, with a shoe covering part of the pole-tip iA] 
the air-gap. 



Tlieorj of the Ayacbroi 



Let R = resistance of whole circuit, 
L = inductance of whole oircoit, 
El r= generator E.M.F., 
E^ =: motor E.M.F. 





refultant. 



Fig. 43. 
Take the origin at 0. 

Let B represent maximum value, 

t = Instantaneous Value, 
«i = Bx sin (« < + i>\n 
eg = ^s sin (m < — ^), 

where « = 2 ir/, and /number of complete cycles per seoond. 

« = *oBln(«« — ^), 

where ^ = angle of lag of i7o '^^^'^ respect to the origin. 

Bf,^ = £}> + j^a* + 2 BiEt COB 2 ^, 



For 



cos 1^ =r — i-= — 2 cos ^, 
-Co 



f.<l;; B\'^'\^*='»^r,^^*, 



— ^» — ^ \ 

8ln^=:l^L±S}coe*. 
V. If© 

B^ and ^ are known, 
Energy shifts the origin by the angle ^. 

e| = ^ sin <b> < — > ^ + i/f>. 



THE SYNCHRONOUS MOTOR. 433 

Sow / = ^ * — — » 

•od /1«gi behind ^o ^7 ^^ angle 4 where 

By intFodneliiff the angle ^ we are referring the E.M J'.'s of both maehinee 
to tbe lero pomt of the resultant waye as origin. 
Inffemeral 






vbere P = the power in watts, and 

9 = lag or lead of / with respeet to JS, 
E and /are mazimiun Tallies, 

T= - f or the periodic time. 

lifit A = power giren to the circuit by the generator, 

P^ = power absorbed from the circuit by the motor, 

Then 

TJ^ 2 V jp -f »a /;» 

A =^-^=^==[cos (* + *)«>8«-8in (^ + ^) 8in«], 

sin « = — » cos * = 



•••^^ = 273?M^^ {i2cos(* + ,^)-Z;«rin (* + *)}. 
and mbsUtuting — ^ f or + ^ we get 

Sow rin,fr = =i£L+^^^, 

If, 

~ i 

BabititQting and redncing 

An angle ^i is Introduced such that 

sin 3 ^1 = . — f and cos 2 ^i = 






1 




^ 



( 



ViP -|. mS xs Vip -I- «a X« 



434 



ALTERNATING-CURRENT MACHINES. 



Substitute in P,, and 
P, i« a maximum when 2^ + 2^' = W 



or 



* + *'=4'' 



that is, the *' sine term " =s unity. 



Ps is positiye provided 



B, 



Et V/p + «az> 



the 



I. 

i 




^:2 



ncLO 



I 



Fia.44. 



which BhowB that it is possible to hare E^ mater than E^ if there is 
proper ratio of resistance and reactance in the circuit. 

Kow, if we plot from an actual motor the 
armature current and the field excitation we 
get a curve shown in Pig. 44. 

This shows that the armature current 
varies with the excitation for a given load. 
The flatter curves are for Increase of load. 
Point a shows under excitation, 
6 shows over excitation, 
c shows the excitation which 
makes the power factor unity ; it is well 
from the point of stability of operation to 
slightly over excite, and this makes E^E* , 
s^ also counteracts the Inductive drop in 
the line, thus showing that the action of an 
over excited synchronous motor is similar to a condenser. 

Graphical treatment. 

Eg = generator E Jf J*. 
j?«i = motor E.M.F. 
E9 = resultant B.M J*. 
/• = resultant current. 
01§z=. projection of /• on O ^ 
O Im =: projection of A on O Bm. 
O £# =r w# = energy given 19 by 

the generator. 
OBm = <*«• = energy abaorbed by 
the motor from the cir- 
cuit. 
, is negative, which shows that wm is the 
motor, because it is Uking energy from 
the circuit f and similarly «■»« is the gener- 
ator, because O Eg . 01$ U positive, and 
gives up energy to the circuit. 

[For further discussion see Jackson'i 
Alternating Current and AtternaHna Cuf- 
rent MacHtnes; also Electrical Wond for 
March 30 and April 6, 1896, by Bedell and 
Eyan. The latter is the classic paper on the subject.] 




01, 
Olm 



vuMfovnm 



FlO. 46. 



OTlTAMOTOIiA. 

These are of two styles, one for changing direct current of one voltage 
Into direct current of a different voltage, and usually called in America 
motor-generators; the second class chanRes alternating current into direct 
currSt or vict verta, the voltage not being changed excepting from alter- 
nating Vmean* values to direct-current values equal to the top of the 
alternating wave ; these latter machines are now called rotary converttn^ 
and are largely used. 



DIRECT-CUREENT BOOSTERS. 435 

lyynamoton are now lazigely used In telegraph offices for redncinjr the 
preesore of the supplj current to roltages suitable for use in telegraphy 
and for ringing and charging generators In telephone offices. 

Theory. I/et 

B = Toltage at motor terminals. 

e = voltage at generator terminals. 

/ = current in motor armature. 

II = resistance of motor armature. 

N* = number of condactors in motor armature. 

L = current In generator armature part. 

it = resistance of generator armature part. 

iv«j=r number of conductors in generator armature part. 

-ir-= ^ = eoefflcient of transformation. 

S = induced E.M.F. in motor part. 
Bx = induced E.M.F. in geuwator part* 
K = r.p.s. XN»x^, 



B^ = ej- n.Iy 

he ^E^kl—krJ^. 



If it be assumed that losses by hysteresis and eddy currents be negligible, 
or that £/= ftA whence A = it/, then 



= f-(«.+lK 



Boeh machines run without sparking at the commutator, as all armature 
rsaetions are neutralized. 



DutKcx-ciJRiftflmr booatsma. 

litis Is a trpe of motor generator much in use for raiting or lowering the 
p fss sme on long feeders on the low-pressure system of distribution, and is 
to be found in most of the larger stations of the Edison companies. It is 
also mncb used in connection with storage-batterv systems in charfflng cells. 

Hm ^ booster " consists of a series generator drfyen by a motor direct con- 
Bscted to its armature shaft. The terminals of the generator are connected 
tai series with one leg of the feeder ; and it is obyious that the current in the 
feeder will excite the series field Just in proportion to the current flowing, 
pnrrided the design of the iron magnetic circuit is liberal enough so that 
we field is way below saturation (on the straight part of the iron curve wav 
below the knee). As the armature is being independently rotated in this flela, 
it will produce an E.M.F. approximately in proportion to such excitation, 
which B Jf .F. will be added to that of the feeder or will oppose that E.M.F., ac- 
endlng ss the terminal connections are made. On three-wire systems two 
generators are direct connected to one motor, and for convenience on one 
Ded-plate. 

Such a booster can be so adjusted as to make up for line loss as it in- 
ersaaes with the load. 

One danger of a booster that is not always taken into account is, that if 
die sham of the driving-motor should happen to open, or, In fact, anything 
should happen to the driving-motor that would result in its losing its power, 
the generator would immediately become a series motor, taking current 
from the line to which it is connected, and by its nature would reverse in 
direction of rotation, and increase in speed enormously, and if not discon- 
neeted from Its circuits in time would result in a complete wreck of the 
machine. It is always safest to have the generator terminals connected to 
their line through some automatic cut-out, so arranged that should 
the shunt break, as suggested, it would actuate the device, and automati- 
eally detach the booster from the circuit before harm could be done. 





436 THE BOTARY GOKVBRTEB. 



A rotarp converter is the name giren to a maohine de«igiied for changing 
alternatlug currentB into direct currents. If the same maohine be used 
inverted, i. e., for changing direct currents into alternating, it is some- 
times known as an inverted converter. Again, if the same machine be 
driven by outside mechanical power, both alternating and direct carrents 
may be taken from it, and it then becomes known as a double current 
generator. 

Theoretically the rotarv converter is a continuoua current dynamo with 
collector rings added, which are connected bv leads to certain parts of tike 
armature windings, sometimes at the oommuiator segments. 

In the following flgure, which represents in diagram the eingle^kaM€ 
rotarv converter^ the collector rings r and r^ are connected by leaos to di^ 
metricallT oppoeite segments or coils of the armature at c and c,. It is 
obvious that as the armature revolves the greatest difference of potential 
between the rings, or maximum E.M.F.. will be at the instant the segmento 
e and c, pass under and coincide with the brushes B and Bi ; and this 
E.M.F. will decrease as the rotation continues, until the lowest EJiJP. 
will occur when the sennents c and C| are directly opposite the centre of 
the pole-pieces P and /*x> 




; WTMT OONVUm 



Fio. 48. 



The maximum alternating E.M.F. will be equal to the direot-euneBt 
voltage at the brushes B and B^, and if the maohine be designed to produes 
a sinusoidal curve of E.M.F., then the alternating B.m!f., that is, the 
Vmean> or effective E.M.F., will be, 

V2 

where e = Vmean' value of the alternating E.M.F., 
and E = direct-current voltage between orushes. 

In a bipolar machine the frequency = r.p.8., and In a maohine with/ 
poles the frequency will be -^ r.p.s. 

Neglecting losses and phase displacement the supply of alternating e1l^ 

rent to the rings must be / V2 = 1.414 / where / is the direct-current 
output. 

If, as shown in Fig. 47, another pair of rings be added, and connected to 
points on the winding at right angles to the nrst, then another and similar 



THE ROTART CONVERTER. 
It. wfH ba pmdnced, bnt In qnadntim to ths lint. Tb* B JI.F. will tw 



Ptor aaeh phue u In ttas •lD(le-plia«e aoBDMtlan preiioiulv ■hovn, 
■cKleedng pbaH dinplHoamsDl mid losHa tbe ourranii wlu b« for 



KInta on tko ummtnra wlndlugL ._ 
^. . , . tlie (ollowlng dlagnun, A Ikmfihatt MiDT*Tt«r li 



Fia. « 

ibteoBBMUoDaof BfbvMtoM rotoir J , 

_^_j _i.t .1. u__' . DUD t i„„ ^, (ollowim 

Ml eoDaator rluf and nentnl point t = —p. = JM X. 

Toltaffo bstiriHUi oollsMor linp (i = ^.^ = .011 X. 



i 



r 



438 



THE ROTARY CONVERTER. 



fl 

t 

u 

B 

t 

s 

e 

i 



I 

fl 

1 

fl 

i 
I 

fl 

d 

fl 





B 
fl 



phase. 


II 

I*' 


q 


•4: 


?I« 


Hi* 

• 


« 


6 


II 


• 


? 


^ 


U 


II 


1! 

i« 


- II 


11 

I** 


• 


II 


II 

i-ii« 


• 

II 

-1? 


II 




II 


II 


II 


1 

II 


•9 1. 


II 


• 

II 


II 


II 


Continuous 
Current 


^ 


M 


Vi4 


v4 






III 

1 


• 

i 


is 

3 





THE ROTARY CONVERTER. 



439 



1 



Thm TsloM of &M.F. and of omrent stated abore are theoretical, and are 
varied In practice by reason of drop in armatnre oondactors and phase 
dinlaeement. In conrerting from a.c. to d^s., if the current in the rotary 
ii m i^iase with the impressed E.M.F., armature self-induction has little 
effect : but with a kuoing current, which may be due to nnder-excitation, 
the induced d^. E.M.F. is somewhat reduced ; and if the machine be over- 
szeited, thus producing a leading current, the induced d.c. B.M.F. will be 
laised. TIm same is the case in oonyertiiig from d.c. toa.c., the a.o. volts 
bdng down on a higgina circuit. 

The corrections for tne theoretical ratios of Toltages as shown are, first 
for drop in the armature ; and second, they hare to be multiplied by the 
fseton shown above. 
Steiamets satrs that the current flowing in the armature conductors of a 
notary is the diif erence between the alternating current input and the cox^ 
dauouB current output. The armature heatinff is therefore relatively small, 
asd the practical limit of overload is Umitea by the commutator, and is 
sbssUt far higher than in the continuous current generator. 

In nz<i>base rotariee the /'it losses of the armature are but 90 % of the 
iwilar i*R loss in the armature as used for d.c. dynamo. 

Kapp shows that width of pole-face has a bearing on the increase in out- 
pat m a rotary converter over the same machine used as a continuous cur- 
net dvnamo. He compares the output of two converters, one in which 
tts pole-faoe is two-thirds the pole distance, and another in which it is one- 
bali the pole distanee. In sinale-phase converters the output is not equal 
to that of the d.e. dynamo, ana two- and threei>hase machines are much 
tiffarent. 

He |rfves, in the following table, the percentage of d.c. output of what 
voQldoe the output of the same machine used as a d.e. dynamo. 



{Cos = l 
9SLzi S 
Cos= .7 

(Oos = l 

nne^hase {Oos= .9 

(Ck)s= .8 

T^or (Se? = ^ • • • • 

toor-phsse jco8= is !!'.'!!!!'! 



Fole-width. 


i 


i 


88% 
81 
73 
63 


05% 
88 
80 
70 


138 
128 
117 


144 

137 
126 


167 
160 
144 


170 
167 
153 



To find the voltage required between collector rings on rotary con- 
Tcrten, when 

T= number of turns in series between collector rings, 
• = flux from one pole-piece into the armature, 
/= cycles per second, 
S = required E.M.F. 



Ihen 



For single-phase and two-phase machines 

JB = 2.83r/»ia-«, 
For three^hase machines 

^=3.e0r/»io-«. 





( 






440 THE ROTARY CONVERTER. 

Ttkt lingle-i^hase rotary haa to be turned up to ByooliroDOiii speed by i 
external power, aa It will not start itself. 

The polyphase rotary will start Itself from the a.c. end, but takes a 
mendous Logging current, and therefore, where possible, It should be started 
from its d.c. side. 

Hie starting of rotaries that are oonneoted to lines baring lights also 



nected, should alway§ be done from the d.c side, as the laxve starting cur- 
rent taken at the moment of closing the switch will surely show in the 
lamps. Polyphase rotaries are sometimes started, as are induction moiOEBy 
by use of a ** compensator.*' 

In starting a rotary, the field circuit must be opened until synchronism is 
reached, after which it is closed. Tlie d.c. side must also be disoonneeted 
from its circuit, as it is obvious that the current produced is altematiK 
until synchronism is reached. Care must be taken to keep the field cireott 
dosed when tb» d.c. side is connected in parallel with other machines, and 
the a.c. side open, or the armature will run away and destroy itself. 

As the change in excitation of the field of a rotary chsmges the d.c. voltage 
but little, and on the other hand produces wattless currents, the regulation 
of E.M.F. must be accomplished by some other method. This can be donehy 
changing the ratio of the static transformer by cutting in and out turns as 
its pnmary, or by the introduction of self-induction coils in the a.c leads to 
the rotary. 

The first introduces a complicated set of connections and contacts, but li 
unlimited in range. 

The second method seems especially suited for the purpose, but is sam» 
what limited in range. Theoretically the action is as follows : Suppose the 
excitation to be low enough so that the current lags 9QP behind the impressed 
E.M.F., the E.M.F. of self-induction laos 90P behind the current, and is 
therefore 180° behind the impressed E3I.F., and therefore in opposition to it 
On the other hand, if the excitation is lai^e, and produces a leading current 
of 90°, the E Ji€.F. of self-induction is in phase with the impressed £3(.F. 
and adds itself to it. Therefore, with self-induction introduced In the a.e 
lines, it is only necessary to vary the excitation in order to change the coo- 
tinuons current E Jft.F. A rotary can thus be compounded by uunjg ^unt 
and series field, to maintain a constant E.M.F. under changes of load, the 
compounding taking place, of course, in the a.c. lines and not in the field of 
the machine, as usual in d.c. dynamos. 

In handling the inverted converter care must be exercised in starting It 
under load, as it is apt to run away if not connected in parallel with otner 
alternators. If they are started from the d.c. side, and hare lagging cur- 
rents flowing from a.c. side, this current will tend to demagnetise or weaker 
the fields, and the speed of the. armature is liable to accelerate to the dan* 
ger limit. 

A lagging current taken from an inverted rotary, even after having reached 
synchronism, will cause an immediate increase in speed, and if enough lag- 
ging will cause an approach to the danger point. 

Running as a rotary, and converting from a.c. to d.c, the phase of the en- 
tering current has no effect on the speed, this being determined by the 
cycles of the driving generator, nor upon •the commutation, simply innuen- 
olng the heat in the armature and ratio of voltages slightly. 

DoubU-etirrent generatoTi are useful in situations wnere conttnoous cor 
rent can be used for a portion of the day and the current transferred througL 
the a.c side to some other district for use in another portion of the day, 
thus keeping the machine under practically constant load. 

The sise of €touhle-<mrrent generators is limited by the sice of the d.c gen- 
erator that can be built with the same number of poles as a good alternate. 
The heating of the armature depends upon the sum and not the difference 
of the currents, as in the rotary ^ and the capacity is therefore no greater 
than a d.c. machine of the same total output. 

Automatic compounding of double cxtrrent generatore is scarcely feasiUe 
in practice, and the field must be very stable, as the demacnetixing effect of 
the lagging a.c. currents tends to drop the excitation entire^. Such maehinef 
run better separately excited. 



BOTART CONVERTER WINDINGS. 



no.4S. 



flu loUoiriiig dlacnuD ahoin the cDanaotloiu of the thres collector riugi 
BtlHeoBtlniioiuourTeDt winding of » Bli-pole d^iiainu. As in the lutSg- 
Mi Uia rtugi u-* oooDMted (o pulut« on tha comniutktor Bt nwrlr aqiU- 
■Untpdnia. 



i 



( 



442 



ROTARY CONVERTER CONNECTIONB. 



^ 






CoMTerters. 

In the use of rotary oonverters, two or more of these machines are 
times oonneoted in multiple to the secondary of the transfonners, and thdi 
direct current leads then oondnoted in multiple to a common bua-har elrevM 
aa shown in Fig. 61. 

INmATOR 



(wmismov) 



•TATIO 



\msmsmm 



mrnmm. 




mm vms 



rOr rO^ 



MfTARy ROTMr 



3 



FlO. 61. 



FlO. 52. 



With the above connections, currents are often formed in the rotaries that 
disturb the point of commutation, and it becomes practically impossible is 
adjust the brushes so they will not spark. Rather than connect across fit 
the above manner, it is better that each rotary have its own transformer, or 
at least its own secondary on the transformer, as shown in Fig. 52. 

CvrreMt DeMaltl«a. 

Current leads ./hmi brushei to binding-potts, must be ample to produce as 
appreciable drop in voltage. The following table gives current densitii^ 
etc., for brush-holders, conductors, bolted Joints, and switches. 



Arer«f« Can«Ht JDe«sitlea for Croaa ftecttOM 

Sarfisce of Variowa Blateiiala. 





Material. 


Square Mils, 
per Ampere. 


Amperes per 
Square Inch. 


Cross section 


Copper wire . . . 
Copper rod ... 
Copper-wire cable . 
Copper casting . . 
Brass casting . . 


600to 800 

800 " 1,200 

OOO " 1/K» 

1,400 " 2,000 

2,500 ** 3,900 


1,200 to 2,009 
800 •• 1^ 

i/no " 1,M 
600" 700 
300" 400 


Brush contact < 


Copper brush . . . 
Carbon brush . . . 


6,700 " 6,700 
28,600 " 83,600 


160 " Iff 
30" « 


Switch jaws 


Copper — copper . . 
Bra» <ar. : 


10,000 " 16,000 
1 20/)00 " 26,090 


67 " lOOl 
40 " m 


Screwed contact 


Copper— copper . 


6.000 " 8,000 
1 10,000 " 15,000 


120 " 90d 
67" lOil 



THE STATIC TRANSFORMER. 



RJEYIBED BY W. S. MOODY AKD K. C. BA^NDALL. 

Tbk itatle traiMf onnet is a deTioe med for changing the Toltage and our 
mt of an alternating circuit inprcMnre and amoant. It consiBti, emen- 
tially, of a pair of matoally inouctiye circuits, called the primarr and 
Moondary coils, and a magnetic circuit interlinked with both the primary 
and secondary coils. This magnetic circuit is called the core of the trans- 
fMtner. 

The primary and secondary coils are so placed that the mutual Induction 
bctveen them Is very great. Upon applying an alternating voltage to the 
primary ooil an alternating flux is set up In tne iron core, and this alteniai- 
ng flux induces an £.M.F.ln the secondary coil in direct proportion to the 
ratio of the number of turns of the primary and secondaij. 

Technically, the primary is the ooil upon which the E.H.F. from the line 
orioorea of supply is impressed, and the secondary is the ooil within which 
asfaidaeed KMIT. is generated. 

The magnetio circuit or core in transformers is composed of laminated 
ibeet iron or steel. The following cuts represent aeonons of seYeral dif- 
fasDt types of single phase transformers. 



_R H 

U 



_ ■ t 

- %^ 




/ — s 






Fio. 1. Gores of some American Transformers. 

p » primary winding ; • « secondary winding. 

In those showing a double magnetic circuit the Iron is built up through 
sad around the ooijs, and they are usually called the *' Shell" type of trans- 



{ 



former. 



448 



r 

444 THE STATIC TRANSFORMER. 



Fia. 2. Unfiniibed ukd Fiuiibed Coila liir Cora Type Tnnafanun. 



V 



Fm. 3. nnnoidied Mid Finkhad Coil* for Bhell Type 



Fls.4. SbflllTyp*Tniufonii« Pm.S. Cora TnM TnnatociM I 

in FnxMBB of CoDsttuctioa. ip ProceM ofConMnutioD. | 

i 



DUTIES OF TRANSFORMERS. 445 

Thofle huTing a stnsle magnetlo dronlt, and haTing Ihe ooils built aroimd 
ttie long portions or Tegs oftbe core, the short portions or yoke connecting 
ttMse legs at eacb end, are called ** core " type of transformer. 

The duties of a perfect transformer are : 

(1) To abeorb a certain amount of electrical energy at a given yoltage and 
free aency, Mid to give out the same amount of energy at the same frequency 
•nd any desired voltage. 

Ci) To keep the primary and secondary ooils completely isolated from one 
iDoCher electrically. 

(3) To maintain the same ratio between impressed and delivered voltage 
al ail loads. 

The commercial transformer, however, is not a perfect converter of energy, 
iltboiigh it probably approaches nearer perfection than any form of appa- 
ntiis need to transform energy. The diilerence between the energy taken 
fato the transformer and tluit ^ven out is the sum of its losses. These 
kMB«s sre made up of the copper loss and the core loss. 

The core lose is that energy which Is absorbed by the transformer when 
the teeondarr circuit is open, and is the sum of the nysteresis and eddy cur- 
rent loss in the core, and a slight copper loss in the primary coil, which is 
IBDenlly neglected in the measurements. 

The hysteresis loes is caused by the reversals of the magnetism in the 
iron eore. and differs with different qualities of iron With a given quality 
of iron, tliis loss varies tm the 1.6 power of the voltage with constant fre- 
qsency. 

Steinmetz gives a law or equation for hysteresis as follows : 

»^a= ^ (»*••• 

Wr=z Hysteresis loss per cubic centimeter per cycle, In ergs (= 10~* 
joules). 
i| = constant dependent on the quality of iron. 

U j|^=r the frequency, 

y = the volume of the iron In the core in cubic centimeters, 
P z=z the power in watts consumed in the whole core, 

ihn i>=i|JV K(B»«ia-% 



uid ■ = 



In the eonstniction, the eore loss depends on the following factors : 

Magnetic density, 

We^j^ht of iron core, 

Frequency. 

Qnauty of iron, 
^ Thickness of iron, 
(fl) Insulation between the sheets or laminations. 

The density and frequency being predetermined the weight or amount of 
Iron is a matter of design. The quaUty of the iron is very variable, and up to 
the present time no method has been found to i^anufacture iron for trans- 
bnnen which gives as great a uniformity of results as to the magnetic 
ion«s as could be desired. 

On the thickness of the laminations and the insulation between them de- 
pend the eddy current losses in the iron. Theoretically^ the best thickness 
of iron for minimum combined eddy and hysteresis loss at commercial fre- 
fiuncies is from JOW to jOV/^ and common practice is to use iron about 
JM4'' thick. 

The copper loaset in a transformer are the sum of the I*R losses of both 
the primary and secondary coils, and the eddy current loss in the conductors. 
In any well-designed transformer, however, the eddy current loss in the 
nndoetors Is negligible, so that tne sum of the I*R losses of primary and 
Meondary eac be taken as the actual copper loss in the transformer. 

* Bedell, Kldn, Thomson, Else. W., Dec 11. 18B6. 




I 



THK STATIC TRANS FOBHEB. 



Practice)!* ftll iuoBSHful ialgni ol truuformera ue dal 
oieaCer or leu eiunt by the method ol cat uid trT. Emntrl' 
■re ul little laloe U the deilgner can obtain data on otber inco 
formen for the Hame kind uf work, uid bue Itie oalcolatloiu 
aMvatna on the behsTlor of the old irhlle under te«c. 

Let S ^ Vmean' of the induced E.M.F. 

A = Kctlon or miimetia circuit In aqoare Inolie*. 
J/= Frequency In cyclea per ascond. 
T^ total luroi of wire In MTlu. 



Thenr = — ^ — (1) 

ThiB equation ifl baaed od the awunptlon of aalne Tsreof eleetroniotin 
force, and li the molt tmporluiC of the formnlaa n*ad in Ui« dealsn of la 
al taroBtl as current tranalonner. 

By Bubatltutlng and tranipoaing ire oan dariTe an equation Anany oa- 
knovn quantity. 

Tbni It the TOlla, frequency, and tumi are known, then — 



«X W* 



W 



4.M X^XT 

(&'■ A W 

iMxffxTx (B'* 

■t once the croae aflctlon at Iron nscewaiy tor the 
knawn, we b»Te, tmnapoelng eqiutlon (4), 



' core, and dengllj ar* 



^ 



FEATURES OF DESIGN. 447 

Fig. 6 if ft «iiiTe gtring the total flaxea m ordiiuttas and oapaoitiw la K. W* 
M aSticAmm. Thto eonre represents approximately oommon praotioe for a 
Hm of lighting transformem, to he operated at 60 oydes. 

For anj other frequenoy or for power work, a onrye of total fluxes can be 
4nvn after three or more transformers have been oalonlated with quito 
fiddy dliferlng eapacities. 

MMfe ti c deiMltlce in the eores of transformers vary considerably 
Tith tSe different freqnencies and different designs of rarious makers. The 
fnctiesl limils of these densities are as follows: 

For 26 cycle transformers from 60,000 to 90^)00 C.G.S. lines per square inch. 

For 60 cycle transformers from 40,000 to 60,000 lines per square inch. 

For 136 cycles from 30,000 to 60,000 lines per square inch. 

Densities for other frequencies are taken in proportion. 

Cmrrmmt lieaMdtiea* — Current density cannot be determined except 
; Beoonsetion with the coil surfisee exposed for heat radiations, and if, there- 
fan, for sny reason, different portions of the winding hare relatively differ- 
est smounts of exposed surface, current densities must be adjusted to give 
' tqusl best distribution. 

FBAXIJltBS OF ]»C9I«ir. 

In tiie design of successful transformers the principal features requiring 
itUstionare: 

(1) Quality of insulation between primary and secondary windings* 

(2) Temperature rise, 
C3) Regulation, 
(4) Efficiencies, 
15) Agring of iron or increase in core loss, 

(6) Power factor and exciting current, 

(7) Cost. 

■ KneuilatioB. 

. No losture of a successful transformer should be given more considera- 
tion tl)sn the quality and durability of the insulation used to separate the 
two vindiiigB. Good insulation means few bum-outs and interruptions ojf 
Mnrice, safety of customers, and low maintenance. The failure of the 
fliwlition is mtal to the primary function of the transformer. 

Not onlv must the transformer withstand the strain when first installed 
V tcrted by the manufacturer, but during years of continued use after 
oast mbjected to frequent overloads and probably high temperatures 
BMOort periods. 

No msnlating material has been found which fills the purpose outlined 
wore BO well as mica, first, because of its l>eing fire-prooi, and second, 
Mcauae of its high dielectric strength. In a construction where there are 
>o sharp comers to insulate, no insulation can surpass mica. 

Next in value as insulators^ are perhaps varnished or oiled cloths. The 
^se of such insulation varies greatly, and depends not only u|>on the 
luUty of the cloth, but more especially on the qualities of the varnish and 
^ oaed in their manufacture. Their particular value over mica is their 
mptability for use with coils having sharp or abrupt comers or edges, 
^iwr, preesboard, fuller board, or other artificial boards are lowest in 
theaeale of insulations, and are generally used not so much as insulators 
*> lor mechanical separation. If treated with oil or varnish, however, ^ 

tliar usulatiDjg value is greatly increased. ^ 

For very high voltages no better insulator is known than mineral oils fH 

I*op«ly refined. Oil-filled spaces insulating great differences of potential ^ 

•"wl be sub-divided by partitions to prevent bridging of the space by n 

eradueting material. 



T«aapenit«r«. 

ftstwne n t s regarding temperature rise and method of determining the 
is me^mam little unless all the conditions are considered. Measurement 
M temperature by thmnometer is superficial and of little value. 

'[JjrauiU transformers in which relatively lar^e coil surface results, the 
'""VMBMore tise is quite uniform, and there is little possibility of any 




I 



448 THE STATIC TRAN8PORUER. 

locml hifli tompflrature [n uiy pvt of tha vrindinjifl. Tempetmlim a 
ured by the rm»l»ri«i method or thermr — "- ' — ~— 



ftmp«r«tiire It to prorido Ijboral dueU between ftdiacent poitiozu of the 



On lergs tisnafonnen the only •((««!¥« tnetbod of innrinc unilona 

. „. — ... . ;j- 111 ■ J,.... between adjacent poitiona of tin 

i the core. Such docta (rstlr 

perienee hafl ibown their neeeei it f, 

I, trangformen an cnxip^ >■ 

natural draft and ■elf-cooled oi 
~ ' intl DiaR Xtaiura 

rhieh the beat ie diani ^ , , _,_ 

.... circulation of which ia generated by the rin in teniperatnre o( th« 

ait itedf. Such traneforoiera are i' — "-■ ' -■ — -— ■-^ -■ 

are expenuve becwiee of the larte i 

Oll-C**led' TruaferKcn. — The oil-oooled (luifbrm 
which the heat 'a diiaipated by the oil circulatins throuch the 



Fla. 7. 176 K.W. Oil-Iniolated S- 



> rapid eoDdH- 
udttie umf 



OIL-COOLED TRANSFORMEBB. 4 

buuiated trmaofomka-, in which tha oil haa flowed in ftud r«pftir«d th* 

- —^ '"h wu Un uhaII to Gbiue immcdi&ta '' ~ 

E may b« elTvctJTcJy Lacrcasfld by m 
eomutiom, Ihua lAfg^y iacreaiini 
in FliT^S wrVB to lEow the etf«cl 
tbi oae of oil- Curre 1 repnAflDts the temperature 

mm 5. th* biffheot temperature rise acceoeible lo thermometer, 
■no] temperature by roisianoe je shown in curve 4. 

TliiM ciovM show very totdbly the value or merit of meanir 
tBapntors rise of trauiionura by rceiatance method latbei t 



AmDDmeter. Tha dilFer«nc« of temperai 
•itb and without oil ai aliDwa in Ibue c> 



^b^ 



.„_. BUffieient rtdiatinj enrfa™ 

~>wt be had in the tank lo disaipale the heat, it becomes necHsary lo 
pievide aniBeial cuewu for awling the Hune. The principKl method* 
npkiycd are the useof a forced blast of air and by the circulation of water 
tbigu^ (be coils immenwi in oil-oooled transformers. 
Tbe brmcr am known u air-blaat traosfortners and the latter as waters 

rs have been built, wherein 

rilMlf. 

ucMdln slzea up lo about 4000 K.V., nsliig 

Ab Alr-BlBat Xl«Bs7*raeir, or one In which Tentllatlon and radl- 
•noo of beat Is. by means of a blast or current of air, forced through Iho 
traasformer eoila and dnre, is shown In Figs. 14 and IS, In this trana/ormer, 
ue colli are bnlll op bigh and thin, and asaeinbted with spaces between 
Ihni. Ihe^r being forced through these spsces. Thelroncore Is also bollt 

P»c^ Thlf atrle ol tranafonuBr has been coaslrucled In sixes op to about 






THE STATIC TRANSFOBMEB. 




Fni. 11. 200 K.W. n.OOO-Volt OH-IunUUd, 

S«lf-CaoliDi Tmuforacr. 



WATEB-COOLED TBANSFOEUEBS. 461 I 



i\ 



Fm. 13. Watar-CooM TraiwtoniHr out of Tuk. 



^ 




Fio. 14. 250K W. Singla-PluMAir- Fio. 15. Sectios of Air-Blut I 



EFFICIENCIES. 



■PTMCIBIf CI ■■. 

Tba aSlelenej Dl ■ tnsaformer La ths ntloot tin anlput iraUa totbeinpnt 



ra k>M, Thlcb U nuds up of tha hjfltf 



THE STATIC THANSPORMER. 



'hlla the copper lo«, or ^ff lou, TkrlM u th« iqDkra of the eom 

-■ via Moondmry. H«thodfl for dfltBrmtamg mil bha ^ 

J ... .^_ _>. — jj. uji trwuforaoer tating. 

truufonner la lensraliy worked >l 



dfltBrmtamg mil bha lo«Ma rnr* folly 



^Hrilwd III tba oimpMT oD (ruufoi 

la • tarTloe whare a truufonner _ . ^ .- 

GODDHted to tbe olreult. w In power work, tha sTengs 



>ower worE, uia btotuv or ■■ ■ii-oin vo- 1 

Ita lalUoiKJ et&elenoj. B; "kll-da;" sS- 

Glanoj I* meknt Uie peroeDUge wbieh the enern lued by tha outomat li <rf 

Uia totkl anaitT ■•ot Into the trunf oruer daring twaulf -fonr boon. 

In iighHin work tha tmuformgn ttn nanall; aonnaotod to tha Dutoa oc 



K. W. CAPACITY 

Flo. IS. Compumtiv* tWren of Con Lohm and RapiliAia, 

Sbowiog tbe ImprcTement made In Tnuulbmun iroDi 

igsTto&K. 



AMumln/on iin a^rmge fire hours furflokd the iMai will be fi houn >S 
uid M hQun (tors loH. ^%e cslcnIftClDn of the "altdBT" elBdaoeT eta, 
tberafore, be made by tbe following forr- "'- ' 



All^, eneiwwjr - core !«. X M + fJtX 6 ^-ruli lo«l y 6 ' 
FroTD tbig It <i erldaot that while tor power work or eonttnnoiu full load 

day " efficlenoy aerlonaly, vat In the oeaifn of tranafonnen whleh are 
worked at full load only a atiort time, bat are alwayi kept excited, a large 
core loaa meant a rary low " all-day '* efflolancy. 



UAQNETIC FATIGUE. 



MAHIIWMG VAnciIJE OB AOHMlTe Or XBOH ASH 

•TBBI. 

TbefabjMt of Mflnf » of vut importaaoe. Thenmilt of invcatjntiaiH 
by PmltmoT Gold^n»«h, Mr. Williun H. Mordey and Ur. B. R. Rougct. 
B-A.. lad to tbe following cddcIuuoiu: 

fint. There is uaquectiaiubly Boah a phfioomena mg ftcoing. J|| 

Sw ond. A great ditfsrance eiiata In tha amnunt of BRring taking placa flj 

Third. Thia lnn«iH in the Ion [n a giTcn body a[ Eron ii dapeudeot 
nWy oa Iba tsmiwaturca at which it is ouioUuned. 

Fosrth. Within ordinarr limit! of tBmperature the tsadency to age ■* 
VMt the sroUer the temperature. > jm 

TiTih. Bolt ibeet ited b mudi le« aubjeot to ageing than Hft iheet iron. fl 

Sith. Sheet ited th&t doea not age materially at moderate tempara- « 

tme (below 76° C.) caa be obtaioed, but aJmoat any iron or iteel ages more ^ 

BeTtttb. The real cauae of agdng has not been djieoTered. Many ftt 
I1» lawa goveraiiv it have boen determined, but thare ia much room 
ferthgr itudy and Taveatigation. 



i 



Oi^ 



CHANGE OF HYSTERESIS BY PROLONGED HEATING. 457 



If 

Z 

% 

] 

M 

I 

i 

1 

« 

R 

e 

} 

M 



N 
S 



CO 



G« 






00 






o 

!8 



Is 



O 

I 



o 

S 






.a 



» 



^SS.! 



®g2g 



•lOQQ 04 'CO •Q<-< 
• mSiq to •IQ *IOW) 






»o< 

SI 






i 



I 3 ^-^ 



•O • -OCO W -^ »-l • 



j5c5 



C5 

■d 



■ COi 



3;5 f 



•a 

i 



• 3 t'-ti 



lor^ •00 



CIQO 






SI 

•O' 



•I 









t 



■ 3 ^t? 



Ot*f^ 00 'f^ '^ • 00 "Q 'Q 
U)(0 to •»-» -CO • CO -^ "^ 









^ :!2 



o 

9 



;i 



t 



lib.-** 

O 9 



f-iC) '^lO iQ 'US CO .« 0000 



5°^ 



)tOO 



>0 *0 -Q 



:I2 S^ 

•Oft Oi^ 






bl-e 



1-4 b AS 






JScJ 

<d 



CO« 



lO 'OO >OiO • >0 '»0 Q>0 
O 't^t^ h>OD ' OO '00 OlOl 



s 



' 3 >4-t^ 
<3 1> s ?. 



00 'CO 



»^H ^ •O) 






• • CO ••© • • • .ig • 

• ^( * ^4P • • • • ^m 

• • f^ *^0 • ■ • "CD 






O<-i04 CQ-^O t^ooo Necio fi^fc 



< 



< 



THE STATIC TRANSFORUEB. 



The moat ImporUuit t»etor la tha life of ineandnemt lamp* is > lUsd^ 
Tolto^, and ■ Byfltem of dlitributLoa in wbich tha ngulation of pranure tm 
not malnuUned to within 2% u liable to ooiuidenbls raduction in ths lif* 
and oaadJv-power of ila lunpa. Fur thie ranvja It a hiEUy unportaat tliaX 
the rtffulalioTt, i.e.. tha ohance of voZta^ dua wholly to ohanca of load owt 
tha ■eoondat? of a transfonaer. be maiatained within aa dooa liiniti m» 

In the desi^ of ■ tnnaformar, aood nrulatloo and low oont hua an ia 
diTwit oppoaitLon to ona aoothar whan both ara daairad in tha hifhcat d^ 
crae. For iastanee, ■agumiDs tha danaitleg will not h« obanted in tha itoa 

tha core km ooa-half. The turns of win, howavar. an doubled, and lb* 
naotanoa of tha aoili quadniplad, bacauna tha iwiatanM chiuicaa with ttie 
aquare of tha turaa ' '— 

A wrt- ■ ■ ■ 



Inted inuHformer, howavar, should siva (ood naulta, both ■■ 
ioaa and regulation, tha nlatlva valuaa dapcodioc upon tktt 



it la to do, and tha aiao td the Iranafon 



u that tha deal^a of the dlatrihntlng intem hai gnlte a* mnita 

ae madntanMiDe of a ataadr roltase aa doea tbs reffuUUio^ of tbm 
I, and tha proper iwleotlon ot the ali« of tranafonnara to b» 



When tnnafoimeri were tlnC used It wa* tha ouitom to inpplj one for 
Bach bouse, and ■ometlmea two or three where the load was baaT]r. Expe- 
rience and tata soon niade It AFldent that the Installation of oi,e larga 
irKnitormer In place of seieral ema]] one* waa very muoh mora eoODOmkal 
In fl rat cost, running eipi^nsee (cost of power toanpply lon>,and regulation. 

'H'liere trans form Bra are supplied one for each bouia, It 1* naceaaarrta 
proTlde a CBpacIt; for 1)0% ot the lamps wired, and ollowtng an OTerload of 
WH at t Imea. Where one large Iranstornier la liutalled lor a gronpof hoaaaa, 
capacity for only B0% of the loUl wired lamps Dead he provided. For red- 
deuce lighting, where the load factor Is always Tery low. It Is often beat to 
runallneof tecoiidaHss over the region to be served, and ooDnectafew 

A study of the folluwlng cunea will show In a measure tbs reantta to ka 

curve. Pig. ^, shows the relative ciist per lamp ur unltot Itansfonngra ot | 
dllterent o^wlty, showing how much cheaper large ona aia tbaa smiU 



no. 3S. BalMlTe Cost ol Trantf ormen of Dlffervnt Oapaeltle*. 

id set of curves, (Fig. 23). shows the power aaved at ditferoit 

Vnctor is tha ratio of tha actual watts in a line to the voJt 
amparea or appannt watta in that line. It is alwj defined as the eoalna td 
the ancle at phase displsoemaDt ot the eumot from tha voltac* io tha 



loads. 




1 



SWrxMA TBAIflVOVmB. 



^ 



Fia.M. Sbop TMliic Sat. to 12, 
nntM. Soeh iipp«»tu« ■■ «m"'-.ILv 
ID tioM th* nu-kiDC pnman. li 



Volb by 300 Volt SU|M. 
— ■— < nC ■ volUfe from 2 to 
therefora, lo build luch 



THE STATIC TRANSPORUER. 
T tiish voltascs, gona hkvinc bean nude lor piuMiuw. 



IS 600.000. 

.r the Hvsre Daiun 
kl tbtx mom thui ol 




FM.SI. 

mom potantUI (train 



pfOTidtti bMw< 

typ* ol dvdgn, I 



TESTINO TRANSFORMER. 






I whJBh an sonneeMd to th* (nuiid 
Bdanl from the tftio induosl by tb* 



typ« ot thii sppliBose, Fin. 24 knd 3B show* 

ihoviDi ■ s«t for modentvly hi^ To]tac«, 
tbt ontv nrmi<4;i>>] w(y of nHniriiic tiM Ufh potatld pcHrMed hj 
y spvL-gap Bhunted uroaa '^' "■ — —'--'- -' '*-- 




i 



Fm. 36. a. K. C. Hi(h Volt«ce Teitinc Brt. 



wk-gsp is B«t lor the, desired roltaca by 



i 



with the ipuk-gap to 
It should the potcntikl 
■ocuiDulUioii o( bich 



THE STATIC TRANSFORHEB. 




Mriaa, ud ■ ooDttant et 



,_ J mMntaliied In the primary. Thl* Ii ihownb 

dlBgrkm In Tig. M. Serin tranetomiera for thie pmrioie ban narer beaa 
Terj nooeutol, due M the tnnible aaaud bj (he nae ot poaentUI la tka 



TYPES OF TRAN8FOBMERS. 



463 



MMondary wh«n opened for any caiite. Various derloee (Fig. 38)» saoh u 
■bort-cirevitiiis polnto aeparaied by a parmfBned paper, or a reaetife or 
ehoUzig-ooll connected across tlie secondary terminals, lutre been Intro- 
duced to prevent any complete opening of the secondary by reason of any 
defect in the lamp or other deylce oonnected in the circuit. 

BeactlTe ooils used as shunt devices hare been used under dUfereat 
names; as eompensators, choking coils, and economy colls. 

A deyice of this kind has been Introdnced by the Westinghouse Electric 
and Mfg. Gompanr, and others, for use in street-lighting by series Incan- 
deseent lamps. It is shoim diagrammatioally in Fig. 29. The lamp ia 




r ^ r ^ r°n 



CONSTANT 
CURRCirr 



C3 — CS 



1 



FlO. 29. 

placed in shunt to the coil ; vhen the filament breaks, the total current 
panes through the coil, maintaining a slightly higher pressure between its 
terminals than when the lamp is burning. It is thus eyident that the regu- 
laUon of the circuit is limited, due to the exoesslTe reactance of the coils 
vhsn several lamps are taken out of circuit. 

Se«BOBB J €7«lla or CoHipesMaiers. 

A modifloatton of the above is built bv several companies for use on ordi» 
aary low potential circuits, where it is desired to run two or three arc 
lampa. It Is a sinale coil transformer, and is shown in Fig. ao, and dlagraro- 
nutically in Fig. H, same page. If any lamp is cut out or open-circuited. 



D. p. FUSE SOX 



COMPENSAXOa 



•.^ 




S.P.SWITCt* 






Fio.ao. Arrangement of Apparatus for Fio. 31. Westinshouse Econ- 
use of Economy Coil or Compensator. omy Coll, for A.C. Arc Lamps. 

the current la the main Hne decreases slightly. As more lamps are out out 
the remaining lamps receive less current, ana it is necessary to replace the 
bad lamps in order to obtain normal current through the circuit. 



THE STATIC TRANSFORMER. 




BO deelgned that ttiere li tt IcKkpcv 

pkth for th« flux betveen thn pr1mmr7 

] wid woondiiry. This la BbDiiii Is (ks 

^ diaffnun at a and 6. At opeD BAOODd- 

U tlltls or no tCB- 



Isakagfl MroH thIapMh, kud If properlj proporttonnd.thU Makagawlll — - 
u regnlata tha carrent tn tba MCondftrT, m> tbal It vlU be approilmaulj 



throocb tha 
there li this k 






««a«inU BIsetrtc C*K>titBt CarrCMt TnaasforHen. 

irormst thna dncribad hu tha dlaikdTantua that Ita ranlatloB 



. . ■« tha dlaadTantua that Ita ragal 

la flied far uir tniuformac and ma; mry In tiwuronnsra of tSs 

deaion without bht ready loeana of sdjUHtment. The Iranafomier ■> 

regiuMee (0' mDitant onrrant oTor bni a llralted nwge Id tha aeeundi 

The General Electrie Compuy eomiant-ourrenl tnmsfanner ihovn 
Figs. 3E and 38 ia eonstnioted inth movable oeooiuiary ooili. and fixed p 
DUUT oihIi. 




Fio. 33. Constant-Cumnt Timna- 
former ihawing CounterweUht 
and PrimRry and SecDodary 
Lmda from WindioE- 

The weight of the movabia mil i 
normal I ull-l»ui, currant the moyah 



Fra. S4. Conneotlan* for Altar 
Beriaa Encloaed An 
■ Syatem, with 80, TS. 



Li(h% 



lially 



IBM 8y»t«n, 1 , 

I Osht Tnnsformar. 

larbalanoed. a< 



Uiua entirely aulomatic. and is fo 

eunant, or a dmiartara from oonatant rjurrent if deeirad. 

SBo be adjuatad for ticBctioally eonatsnt ounaat tor pi 



.. . T^-<J"Ki 

inf the magaetjo repulwoii bctwea 
ape are out ol the oireuit. the Id 

(Bee Fin, Sfi anil 38.) At mid 
a im maximum. The reflulation i 

if deeiiadTThatra 



Jktku: 



TTPE8 or TBAHBrORUKBS. MS 

■d to \itb% kub. or for ■ iMaliva ngo- 
D luQ load to ligbt kwla. lUi tdf^t- 



1 




w a obiidsad br diuidna th* pod 

i^lbBinmiipendfld. Tbaourvaili 
iildWi^i tnoifontier. 
^ • * aidcMd in a 






m in FU. 37 iliow tbe nags obUinsd 
iiuD or ah«l Inn lan^ filled with 
t ol the secondary ooib. 









1 












^ 




r1» 


^ 


.,.00 




;■ 








asaa 


ea 


il 












TTl 


KM 


«. 


«. 












= 


LU 


2! 


ItkS 












— 


^ 




"^ 






!, 


T.r 








-*- 


' ' 








' 


i., 








_J5S^ 


















































































































^* 






























"ni^ B^tfS^^eed by ■ weifdit ot 
25?»'^of IheremtaWr. '^ ^ 
nfM d the tioib. but alow api: 
" - ■•OBJ to 



tnuafotmer the moTubls ooll Ig 

nnnthtftr Tnnvnhltt OOl], dependioc 

<rtant at Btartinc 



BSD. '^!s'de™''taiir 

type is piBclicslly the ume u that 
the nnu atpscity. The pmnr [set 



< 



THE STATIC TRAN870RK&B. 



For Low Toltaie oirmiitt required on ti 

ooniUknt-oumnt trmiufonneT Ufl been d ,_.— .. , 

•DimMUd IB Hdee with the line. Fig. 38 tfaom k typical a 



Pn-SS. aecdlBtincReMtukeaOaDbrllaDlutMn OeocnlOanalnietionCa. 

adopted by one of the leadina nuuiufacturen. It oonriate of ■ lioKle nil of 
iDiiUkted wire vruised to indoM more or leai of one leg of > " W^'-ehaixd 
magoet ej ihuwn in the foUowini cut. Tlie coi] is nupendcd from one aid 
of a law and counterbelnneed bf 
■ wd(ht on the other, and m 
amaaed that at all poiote of iti 
traveTU juM balancea the T«ryiii( 



. lie eon with a - — 

to optD the circuit. Without ciB> 
I rent flowina. the noimaJ poftilion 
I of tlw ooi] ■ at the top or oS Ibl 
!«■ of the mapiat. When the 
■Atdi ii (ioMdr eurreot flowi ia i 
the eirsuit (and «oil). and dran j 
the ooil down oD the l<c to a poba i 



relheeameED- | 



hoMa the eorreot BtreOKtbat a pn- 
determined point: aa, say, O.S un- 
pnjea. . It ia said that thia deria I 

vithiD oue-tanth ol an ampere. 

Thek»ett-»«h*i*^-.*- i»— «u1 ' 
i*Aloa>«in 

der all eonditioiM ot Iwd. 

Ai it I* not always, or * 
«t«B, that it u DMenary to i 
vide for raculation id ma are _ 
ndt to (he sitral of ila foD haiL 
themakars have adopted the pol- 
«..»..._. ley 0* lupplyiDV inrtmnuol* to 

Se, "0.1." BerleaA.O.BaBulator. care for but that part <4 the load 

that b expected to vary, in lonM 

I 10% of the circuit and in othen 7S%, thiu avddinc the ■>— ' *" 
T appantua. or for iBBulstion for the total - ^ ' 



POTENTIAL REGULATORS. 467 

TbsT claim nuotba- vlTBntsni in being able to oonnKt tha devioa Id on* 
l<« of the neriea cinuit, aod allawing tbe other end of the eireuit to be oca- 






w. 



(^ 



1 altonadnc currenl potantUl nculator i» Mgentiall; a tnarformar h»r- 
ti pfimarT connened aenoa the tnaini, and iti leooDdair In MHee wf A 
nauu. The ■eeondsry ii arranied so that the voLtufe at It* tumiuli 



y particular ran^r 



Dticrambf Connectiona far Single-Phase Potential Reguiatoi, 1 

WeMioshouae Eleo. snd^Ulg. Co. 



468 



THE STATIC TRANSFORMER. 



The MToral different styles of feeder regulators hare been deTisod* differ- 
ing in principle of operimonf but all of them hare the primary coU con- 
nected across the mains, and the secondary coils in series with the mains. 

The " Stillwell *' regulator, which was designed by Mr. L. B. StniweJl, hss 
the usual primary and secondary coils, and effects the regulation of the cir- 
cuit by inserting more or less of the secondary coil in series with the line. 
This secondary coil has several taps brought out to a oommutating swit^ 
as shown in Fig. 40. The apparatus is arranged so that the primary can 
be reversed, and therefore be used to reduce as well as to raise the roltage 
of the line. It is evident from an ol)servation of the diagram that if two 
of the segments connected to parts of the coils were to be short-cirenited, it 
would be almost certain to cause a burn-out. To prevent this, the moTable 
arm or switch-blade is split, and the two parts connected by a reaotanoe, 




KAPP6 MOOIFIOATION 
OP STtLLWlLL REOUlATdl 



Fig. 42. 

this reactance preventing any abnormal local flow of current during the 
time that the two parts of the switch-blade are connected to adiaoent seg- 
ments. The width of each half of the switch-arm must of neoeasity be less 
than that of the space or division between the contacts or segments. 

As the whole current of the feeder flows through the secondary of the 
booster, the style of regulator which effects regulation by commntating 
the secondary cannot well be designed for very heavy currents because of the 
destructive arcs which will be formed at the switch-blades. To overcome 
this dli&culty, Mr. Kapp has designed the modification wldeh is shown in 
Fig. 42. In this rcoulator the primary is so designed that sections of it can 
be commutated, thus avoiding an excessive current at the switch. This 
regulator, however, has a liimted range, as the secondary always has an 
E.M.F. induced in it while the primary is excited ; and care must be taken 
to see that there are sufficient turns between the line and the first contact 
in order to avoid excessive magnetising current on short circuit. 





Fio.48. Connections for M. R. 
Feeder Regulator of G. E. Co. 



Fie. 44. Diagram of Con- 
nections ox Feeder Po- 
tential Regulator. 



The General Electric Company have brought out a feeder regulator, in 
which there are uo moving contacts In either the primary or secondary, and 
which can be adapted for very heavy currents. This appliance is ^plainly 
shown In Figs. 43 and 44. The two colls, primary and secondary, are set at 
right angles in an annular body of laminated iron, and the central ImqI* 



^ 



THBEB-PHA8B REOULATOBS. 



469 



tan ii arranced so as to be rotated by means of a worm wheel and 



chance in the seoondary voltage, while boosting or lowering th^ line 

■ sontinuoos, as is aJso the ohaiwe from boosting or lowering, or 

In this re^ilator, the change ot the seoondary voltafre is effected 

ngs in Oux through the seoondary ooil, as the position of the 

I eore is changed by the turning of the nand wheel and shaft. There 

Nfoce, no interruptions to the flow of current through mther the 

or seeoodary oous, and the regulator is admirably adapted for in- 

It K|^t4ng service^ where interruptions in the flow of current, how- 

mtftneous, are objectionable. 

Mmwtkrmim Ctvcait ]ft«ff«1aion. 

a number of dreuits are run out from the same set of bus bars, 

B of each drcoit is prpvided for by the use of a single coil trana- 

from TariouB points, on the winding of whioh leads are brought out 

^ngaktor head, from which any part or all of the transformer may be 

iBtD isrvioe to increase the pressure on the line. 



Segwlatonk 

Ngnlator deseribed above is suitaUe only for operation on single- 
ckcnits. The primary is connected in a shunt and the secondary 
vith the circuits to be eontroUed. Two or three-phase regulators 
but having either primary or seoondary on the moving 





Fm. 45. Three-Phase Induction Potential Regulator. 

eommonly used. The voltage in such a design is constant in each 
of the secondary winding, but by varying the relative positions of 
rj sod secondary the effective voltage of any phase of the secondary 
^Qfeoit is varied from maximum boosting to maximum low«ing. 

to the diagram which remsents graphically the voltage of a 

i of the regulator, e o — Generator voltage or the E.mIjP. im- 

00 the primary; a o "^ E.M.P. generated in the seoondary coils, 

eoootant with constant esnerator ELM.F.; 6' a* » Seoondary XM.F. 

with the generator ElM.F.: e' a' » Line E.M.F. or resultant of 

E.MJF. and the seconoary E.M.F. 

^eoutraetion of the rogulator is such that the secondary voltage o a 

e to ssrame any desired phase position relative to the primary Ejif.F., 

iZl^h^oc, etc 

>^it8 phase relation is as r e p re se nted by o f, which is the position 

ths north poleo and the south poles of the primary and secondary 

"^ sre opposite, the seoondary voltage is in phase with the primary 

.■ad is added directly to that of the generator. The regulator is 

to be in the position of maximum " ooost." and by rotating the 

with refsrenoe to the fields, the phase relation can be changed 

ttteot b etween this and directly opposed voltages. When the 

of ths seoondary is directly oppoeed to that of the primary or gen- 

[»ite phase relation is as rep r es ente d by o d in the disigram, while o b 

' the phase rdation of toe secondary when in the neutral position. 




i 



( 



r 



THE STATIC TRANSFORMER. 



SASB TBAirsroBMflma. 

immonly uasd "■broad" tot * toaa 

, sd into AnKTiao prutig*. Sutt 

:• differ UtU« from the liiiclA-phHe deeifiu Bud loay be boiH ia 

The tbree^tuae ihell type tnuufonner eonset* dmplv of i 
phsM unite ■□ united thet oorundenkble of the iro- '- * — 
imiininwij Thi* i* iUuatntad by the lollDwioc ei 



dmply of 
I in the o 



i threfr^hve core type trvuformer eonnrt* oF three ie^e of nimfn jitnan 
B treiietoTiaer pidcwl aide fay aide uid united M eithv and by ■ yika 
he Hm* sroee •ection m eaoli ancle-phM* be. 



mil nil 



Fm. tt. OroM BeoUoD of the Oara* and OoUa of Time SiiwIe-PhMa 
Air-BIan Transformar*. 




Fm. W. CroM Swtioi 



jt tha Sam* Coi^i Combined In On* Thi«»-PhaM Ail- 
T of a Capacity Equal to the Total OaMwlty at 
Tbow Above. 



aATlO OF TBANBFOBIUTION. 




ATnrfiwlTIi 



TiiBilDmien ara unially tniih with both their primary 

nih moAd ia two or more ■mUodii in ordsr to faouilats ehAiwv oi timaa^ 
ttoMioo nUio. Thii iM MpMially uMful irli«r« three trudotman are 
■id in a thr««-pbMe ■ystam. Lat 

■ — latio of tnuufomiMioii from one seeUoa of hich-t«uiDn ilda 
to one aeotion of kw-teoiioD aide, exprtaaed ta an iDta(<r; 
''■™Bid« " " " •™ " ' »*"■ 

imbar of aaetiona io aariaa in eaeh aim of the delta, hiah- 



teniioD aide: 



fi ud d, bdoK the evmapoDding qnaotitica tor tlu lev-ten^n aidaL 
_ H.T. line TolU Ys/S + D 

"W* formnik ia applicable to aombinatian Man and daltaa aa wall i 




r 



472 



THE STATIC TaANSrORMBR. 



TRAif AfoiKHJBit coiffirscnrjiOHA. 

Some of the advantages claimed for alternating current STstems of di^ 
tribution over the direct current gystems is the facility with which the 
potential, current, and phaaeB can be changed by different conneetiotui of 
tranaformera. 

On single-phase circuits, transformers can be connected up to chany 
from any potential and current to any other potential and current; but a 
a multi-phase svstem, in addition to the changes of potential and eurreDli. 
the phases can be chaiiged to almost any form that may be desired. 



Mavl«-Phaa«. 

The connections of the 

having parallel connections. 

a favorite method of supp.^ — v-.^,— « ....^.^ ,,— ^ ...i— «- 

three-wire seoondaries. A ti^ is brought out horn the middle of the 





Ffo. 63. Arrangement of Balanoinj^ Transformer for Three- 
Wire Secondaries. 



ondary winding, this tap connecting to the middle or neutral of the three- 
wire system. In this way a few large transformers can be connected by 
three-wire secondaries in a residence or other district, and will take care of 
a large number of connected lamps. 



^ 





ammsmuL 



*-»?»•« »t f ■* 





wsKn |uiiuiii 



y 



-O— 



FiQ. 55. Sind^e-Phase, 

Fio. 54. Single- withThree-WireSeo- Fro. 66. Two- 
Phase, ondary, Useful for Phase, Four 
Residence Circuits. Wires. 




Fio. 67. IbTee- 

Wire, Two- 

Phase. 



TBANSrORHBB CONNECTIONS. 



473 




a modification oi the three- wire circuits, in which the out- 

are fed by a singje tmnsformer. and the neutral wire is taken 

of by A balandng transformer, connected up at or near the center of 
ibotion. The capacity of the balancing transformer need be but half 
taet variation in load between the two sides. 

makers of transformers have the connection board in their trans- 
ao mmngfid that the two primary coils may be connected either in 
paraUcs by mere ehangw of small copK>er connecting links, so 
amaMB transformer can be connepted up for either 1000- or 2000-volt 
and the secondary for either 50 or 100 volts. 



or 



The plain two-phase or qaarterwphaae oonneetiop <Fig. 56) is simply two 
' nuiaformerB oonneoted to their respective phases, the phases oeing 
tirely separate. In the three-wire quarter-phase circuit, one of the 
'b« used as a oommon return, as shown in Ffs. 57. 



. three-phase connections shown in diagram 58 are known as the 
eonneetions, and are of great advantage where continuity of service 
important. The removal of any one transfonner does not interrupt 



^ 



JL JL-I 

twwilaml 





Fio. 58. Three-phase 
Delta Connection. 



Fio. 59. Three-Phase 
Star Connection. 



the thive-pliase distribution, and the removal of two transformers still 
of power transmission on a single phase of the circuit. 
Y or star connection, as shown in diagram 50, has one of the 
of each primary and secondary brouffat to a common oonnec- 
tMm, the rwnaining three tenninals being Drought to the main line and the 
distributing lines. The advantage of the star connection over the delta con- 
aeetion is. that for the same transmission voltage each transformer is wound 
for only 50% of Che line voltage. In high-voltage transmission this admits 
of mncli smaller transfonaen being bult for mgh potentials than is possi- 
ble with the delta eanneetion. 



i 



r 



474 



TH£ STATIC TRANSFORMER. 



MC«BieB« of TnMsformen for Atopptar Up 
for Iionc IMsteneo XnuumlMlon. 

Figares 60, 61, and 62 show diagrammatioaUy tbe oonnectioiis for 
threo-phase transmission to quarter-phase generators, with luterchang* 
and non-interohangeable transformers. 



VCKUUTM 



mr w 




i;::a»«/uJ ™ 

iCBwn (VlffVn rvwmn nuMroMaKP 




V- - —in 



Fio. 60. Changing Quarter-Phase to Three-Phase, 
Non*InterchangeaDle Ste{>-up Transformers. 



QENeRATOfi 



OCNERATOR 




jjUJjulAMfl 



[ 





V 



Fio. 61 . Ghangiiiff Quarter- 
Phase to Three-Pnase, and 
back to Quarter-Phase. 
All Transformers Inter- 
changeable. 



Fig. 62. Changing Quarter- 
Phase to Three-phase. All 
Step-up Transformers Inter* 
changeable. 



^ 



TRANSFORMER CONNECmONS. 



475 



A rotmrj oonrarter wound for 8lz-phM« has a RHMter oapaolty for work 
tfaa sAiDie machine wound for three-phaae. Three-phaao tranamlasion, 
-er, is rery economical, and in Fin. 63 and M is ahown a dlamm by 
•iz pbaaea can be obtained from three phasee by the use of only three 
haosformers. 

Each transformer has two secondarv coils. One secondary of each trans- 
temeriaflrsteonneotedinto a delta, then the remaining secondary coils are 




WWWWVA/V wwvwvvw wvwvwvJ 



^/vw^^ 



l^^/^AA^J^/VV^/sA..p/sA/VV^ 



/WVA/^ /SAAA/>^ AAAAA 





Six-Phase A 



Figs. 03 and 64. Three-Phase to Six-PluMe Connection. 



oooneeted np Into a delta, but In the reyerse order of the first delta. This 
is sn MuiTalent of two deltas, one of which is turned 180° from the other. 
Is the dlagrmm ABC represents one delta, and DBF the other. 





Fio. 66. Diagrams of Connections for Changing from Three-Phase to 

Six-Phase. 

In the same way the two seoondaries can be connected up T, and one 
T turned l$fp to obtain six phases. The disadrantage of Y connec- 
tion, however, is that in case one transferrer is burned out, it is not possl- 
»!• to Qontlniie mnning, aa can be done with delta connections 



476 



THE STATIC TRAN8FORMEB. 



Meth' 



»rcMu 






Wwi^ ^ VM^KMAMf 




Fig. so. Two>Pha«e. 



wvwvw^vw^rJwM^ w www 



AvwvAa>a/\ 

2 



"VvyvAW' 




IlG. 68. Three-PbweJ. 



Vwww^^ w^ammM^ Uwvm^^ 




Fio. 70. Six-Phase I>iameUio«l. 
pAVNAA/WV\2^AAAAAAA^ 



AAAAfVWNA K/yWWVV 




Mrs t# 



U w wwww Umvmww Wmmmv 

f3 



kwVWAAAAAMJ/VNA/Vil 




IflO. 67. Three-PhAM A. 




Fio. 6B. Three-Pbue Y* 

^fMMfMl wNmMi Vmm im 
1.3 



lv\A/V^yAAAVSMf>NAAA/) 




Fig. 71. 8ixrPhM«A. 

P.I.Kttllf VWWWVWVVv* vVWWIVvVv 

V//W^^» ^^A/W^a l^AAA^M^ 



VNAAA /W\AA A(W\A 




Pig. 72. Siz-Phase T. 



Fig. 73. Siz-PliaaeY- 



GONVEBTER AND TRAN8F0BMSB CONNECTIONB. 477 



l...Jl.iJu^ 




I I >1 .■■r"TSasgi 



Fio. 7L ThrM Transfonnen Arranmd in Inter-oonnected Star, Operatiiig 
a n&ree-PhaM Botary Conrerter on a D. C. Throe- Wire System. 

The** Scott" eonnection is used a great deal in transmiwions and dittri- 
bataoiifl (See Fig 75.) One transformer is designated the nuun, and the 
other the teaser. Two transformers are required. They are made exactly 
•Eke, so that with proper connections either nuty be used as main or teaser, 
ns winding is provided with a 50% tap and with taps so that 86.6% of 
U» winding may be used. 1-2-3 are three-phase voltage, A-A' one-phase, 
B-Bf the other of the two-phase circuit. Keference to the small diagram 
rinws the jeaaon for using 86 6% of ^lindins of one transformer; also the 
ity lor the 60% tepT 



Tco^er 




Mafn/OOX 




iooT 



Fra. 76. 




Fio. 76. 



ASHBiiro PowvR wm aix-phask cMncrrxTS. 





478 



TH£ STATIC TRANSFORMER. 



A comtsonoir of vmambwo 

(F. O. BlaelnraU. Trmns. A. I. E. E., 1Q03.) 



AMmninc that three trmnsfonneni are to be uaed for a three-phase pow 
traaamiwion and that the potential of the line is settled, eaoh of the "~ 



formers, if eonneoted in Y, must be wound for —jz or about 58 per esnt of 

the line potential, and for the full line current. If eonneeted in A, eaea 
transformer must be woimd for the line potential and for 68 per eent of ths 
line current. The number of turns in the transformer winding for Y 
connection is, therafore, but 68 par cent of that required for A oonneetioa* 
to avoid eddy current losses that occur when the cross section of the eoa- 
duetor is too lai^e. 

The Y connection requires the use of three tranaformera, and if aa^ 
thing goes wrong with one of them the whole bank is disabled. With tia 
A connection, one of the transformers can be cut out and the other twa 
atill deliver three-phase power up to their full oapadty; that is, two-tbirai 
of the entire bank. 




Fzo. 77. Step-down Transformer for 4000 Volt Y Diatribaftioa. 

Combined three-phase transformers are generally of small aiae, and on 
that account are preferably Y connected on the high poten^al side. 



«rowi«lMc tlie ireatraL 



If the common connection of transformers joined in T is grounded, the 
potential between windings and the core is limited to 68 per eant of that 
of the line. 

Under normal conditiona, the potential between any conductor of a 
three-phaae transmission circuit and the ground is 68 per cent of the lias 
potential, with either Y or A connection, but the neutral may drift ao as 
to inoreaae the potential with an ungrounded ayatem. If *^ ^ ^ '' 



') 




Fm. 78. Step-down Tranaformer for 200 Volt Y 



partly or completely grounded, the potential between the other two braaefaca 
and the ground is, of course, incrMsed and may be the full line pTTtfffti»>- 
With a grounded neutral Y system, a ground is a diort dreuit of the traoa- 
foTBierB on the grounded branch, and the tranamiaaon beoor^-* ' ^-^ 



CONNECnON OF TRANSFORMERS. 



479 



^ 



, Firoiii the poiai of view of nfety to life and unvt o i ion of fim this ia • 
iannble oonoitioii, wpaoiaUy if the low tenaioii dSetribution ie aiao grounded, 
i If the high tenaiott oireuit iD*kee eontact with the ground or low potential 
tgftUan, it can be immediately eut out by funs or automatic eirouit breakers. 
; The difficulty is that a power transmission with grounded neutral b 
^ikdy to be frequently shut down by temporary grounds, such as would be 
icsosed by a tree blowing against one of the wires. E>ven if the circuit is 
'set opsned, the drop in the pressure due to the sudden "short" on the 
fine will eauee synehronons apparatus to lall out of step. 



If two tTmoaformers are oonneeted in series, there is no certainty that 
ttey will diTifde the potential equally between them. A ssrstem in which 
•B the electrical apparatus is oonneeted in Y has somewhat the same char- 
aderistics. The neutral mAv drift out of its proper place and there will be 
■Bsqosl potentials between it and the three conductors of the eirouit, due 
to nequal loading and differences in the transformers or transmission or- 
aits. Such unbalancing would cause unequal heating of the transformena 
sad if a four-wire three-phase system of distribution were employed, would 
Mciooriy interfere with the r^ulation of the voltage. If transformers, 
tlMrcibre^ have Y seoondaries, it is desirable that the primary should be 
A eonneeted. Two systems in common use with which A primary wind- 
Off ihould be need, are shown in Figs. 77 and 78. 



The high potential windings of transformers are necessarily of hif h 
nsetance, and if left in series with a circuit of large capacity, as shown m 
FipL 79, 80, 81, and 82, the leading changing current flowing over the react- 
■nee may set up extraordinarily high pressures. Figs. 70 and 80 represent 
Y-sonaeeted banks of three transformers each connected so as to cause such 




Fia. 79. 



Fio. 80. 



tnae of potential. In Fig. 70 the primary of one transformer is exdted by 
scaerator, the primary of the other two transformers being open-cireuited. 
u Fig. 80 the primary of one transformer is opai-eireuited, the other two 
wing eonneeted to the generator. Figs. 81 and 82 show T-conneoted banks 
« two transformers, wiiich might be used to transform from either two- 
phsis or three-phase to thre^phase or vice versa, and are simibu' in action 
to Fig. 70. If m anyone of figs. 79t 80. 81 and 82 the secondaries are con- 
asetea to a long distance transmisrion circuit, a pressure of many times the 
aocmsl potential will beset up between A and B.and between^ and C, that 
Mtwen A and C not bong affected. 

It is theoretically possible for a potential 100 times that for which a trans- 
fanDSr is wouiid, to be caused by opening the primary switches of one or 
more of the ttanafomiers of a bank connected in Y before the secondary 
■witdies are used. Actually, the current jumps across the insulation at 
some point in the system before there can be any such increase in pressure. 
If thfiie are a number of banks of transformers in parallel, this olkenomenA 
osmot occur except when all but one bank are disconnected. This source 
of trouble coukl be obviated by emptying oil switches on the high poten- 




,1 



/ 



480 



THE STATIC TRANSFORMER. 



tial aide which disoonneet the line before the low tension switdias 
iiBed, or by triple pole switches on the primary which open all three 
of the bank of tnuo^onners at once. 

The selection of Y or A connection of transformers for long 




Fig. 8i. 






Flo. 82. 



transmissions should only be determined after a careful oonaidemtion of 
the conditions in each case. 
There is little choice between Y or A without a grounded neutral. 

NoTB. — For further information on this subject 'see discussion on this 
paper in Proceedings of A. I. E. E. for 1903. 



iAMs EUBCTRf c coimPAinr ansiftciT] 

ARC 



■WWWVWWAr 
TRANeFORMVR 



J 




(By P. D. Wagoner.) 

A detmled idea of the operation of the mercury arc rectiBer drcuit may 
be obtained from Fig. 83. Assume an instant when the terminal H of tbi 
supply transformer is positive, the anode A is then pontive axui the are is 
free to flow between A and B, B being the mercury cathode. Followiiig 

the direction of the arrows stiU further the 
current p ass e s thro^^ the load J, thioqgh 
the reactance coil £ and back to the iM«a- 
tive terminal O on the transformer. A little 
later, when the impresaed dectromotrre 
force falls below a value suffident to mminr 
tain the arc against the counter e l cc t io - 
motive force of the lu-c and load, the 
reactance E, which heretofore 
charging, now discharges, the 
current benug in the same direetk>n 
formerly. This serves to maintain the are 
in the rectifier until the dectromotive force 
of the supply has passed thitray^ aeit^ 
revcr o c e and builds up to such a value a» 
to cauae A* to have a sufficiently posHjve 
value to start an are between it £od the 
mercury cathode B. The disehavge eireuit 
of the reactance coil E is now throu^ the 
arc A^B, instead of through its mmcr 
circuit. Gonsequently the arc ^'B is now 
supplied with current, partly fnon thetTaB»> 
former and partly from the reactance ooil XL 
The new circuit from the traoaformar is 
indicated by the arrows indosed in ciwk B> 
The amount of reactance inserted in tlie 
drcuit reduces the pulsations of the direel 
current sufficiently for sXL ordinary com- 
mercial purposes. Where it is advisable to still further reduoe the ai^ll- 
tude of the pulsations, as. for instance, in telef^one work, Hob ia done with 
very slight reduction in efficiency by means of reaetanoes. 





F E 

Fia.83. Rectifier Conneotk>ns 
Shown Diagrammatioally. 



WESTINQHOUSE MERCURY ARC RBGTIFIER OUTFITS. 481 



!K13r«Hai70iB 



OWJTMTS. 



Thmam cratfita are a development of the conetant ouirent traiiflfoniict 
adapted for uae with the mercury rectifier, receiviiig alternating current at 
e conatant potential, and deliverinc a ooiwtant direct ooRent. By a special 




. OQQQQQQOOQQ R OQQQ JSftQQPQ., 



ra 



TTOnrowrnT ra g ro - dM ' 




Fie. M and Fto. 0. Dlagrama of Weitinghoiise Mercury Arc Rectifler. 

■nannment of coils the usual suetainins reactance is omitted, resultini 
ID reduced floor apaoe and an improved eflidency. A boiler iron tank 
nth cast iron cover, two alternating currents and two direct currents leads, 
dssoibes the simple and rugged appearance of an outfit. (See Fig. 84.) 
, Hie connections (Fig. 85) explain the operation. P-P and 8-S are respeo- 
tave^ the primary and secondary; 8t the starting transformer. R the 
netifier, ana A the auadliary coil for exciting the starting transformer. 













,1 








• 


1 
























^^^ 




r-^ 


1 


t 





Fig. M. 

The oatfit is eiafted by tipping the bulb, causing a spark between the 
tcnninab of the starting transformer as the current path through the 
mereory is intermpted. This breaks down the hi^ resistance of the nega- 
tive deetrode and permits the establishment of the direct current. 

The bulb is carried in a box which b easUy slid in or out between guides 
to the bottom of the containing tank, thus making the buH> r^Iaeement a 
Better of but a few moments. 

Simple variable weights permit of adjusting the transformer so as to 
Mver its exact rated direct current (Fig. 86), at aD ioads. 

The power factor at f uD load averages over 70 per cent and the effidsncy 
watt over 90 per cent for all sises of rectifier outfits. These are regularly 
built in 25, 35. 50, 75 and 100 light capacities, either 25 or 00 cycles, for 
KOO v.. oWoV.. 11,000 v., and lZ,2O0y. eirouits. 




i 



i 



482 



THE STATIC TRANSFORMEB. 



MnRRRnr 




^ili]ili!»lili!»l» 



Fxo.87. Weettnghoose Meronry 
Arc Rectifier for Battery 
Ghargljig. 

for which these outfits are built, 



These outfits are intended to operal 
frtun low constant potential eireuitsaa 
deliver a oonstent D. C. voltage, varyiai 
from 5 to 125 volts, aeoordins to deoiiu 

Fig. 87 indicates a method of oonni^ 
tion which is essentially the same as k 
the arc lighting outfits. SR ia a staria 
reststanoe, for the rectifier; MN, the auB 
transformer, BB* the D. C. terminals, sa 
AA* the A. C. terminals. ' 

These outfits are started by tipping Ik 
bulb. A spark due to interrupting 
current in the starting resistance bi 
down the hif^ necative electrode 
anoe, permitting ^e direct current to I 
established. In this outfit, like the ai 
outfit, a special arrangement of ooils i>g 
mits the omission of the usual sustains 
coil. The D. C. volta^ is varied o 
changes in the connection to the autt 
tranaormer, or by changes in the A.( 
impressed voltage msuie by an adjustao! 
senes reactance. Control i>anels carryis 
instruments, control dial, circuit breiucfl 
etc., are furnished. Thirtjr amperes. 11 
volts, is at present the maximum capacit 
for either 25 or fiO cycle aervioe. 




Althouffb the standard types of transformers of to-day are made on li» 
found by long experience to be the best for all purposes, and are subject I 
careful inspection and test at the factory in most oases, vet t